In situ method for forming thermally conductive thermal radical cure silicone composition

ABSTRACT

An in situ method for forming a thermally conductive thermal radical cure silicone composition is provided. The in situ method comprises forming a thermally conductive clustered functional polymer comprising the reaction product of a reaction of a polyorganosiloxane having an average, per molecule, of at least 2 aliphatically unsaturated organic groups; a polyorganohydrogensiloxane having an average of 4 to 15 silicon atoms per molecule; and a reactive species having, per molecule, at least 1 aliphatically unsaturated organic group and 1 or more curable groups; in the presence of a filler treating agent, a filler comprising a thermally conductive filler, an isomer reducing agent, and a hydrosilylation catalyst. The method further comprises blending the thermally conductive clustered functional polymer with a radical initiator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage of International PatentApplication No. PCT/US2014/015607, filed on Feb. 10, 2014, which claimspriority to and all the advantages of U.S. Provisional PatentApplication No. 61/763,144, filed on Feb. 11, 2013, the content of whichis incorporated herein by reference.

The present invention relates generally to a method for forming acurable silicone composition, and more specifically to an in situ methodfor forming a thermally conductive thermal radical cure siliconecomposition

Polyorganosiloxane compositions that cure to elastomeric materials arewell known. Such compositions may be prepared by mixingpolydiorganosiloxanes having curable (e.g., hydrolyzable, radiationcurable, or heat curable) groups with crosslinking agents and/orcatalysts, as needed. Generally, the polydiorganosiloxanes may have 1 to3 reactive groups per chain end. Compositions including these componentscan then be cured, for example, by exposure to atmospheric moisture,exposure to radiation, or exposure to heat, depending on the curablegroups present.

The cure rate of a particular composition depends on various factorsincluding the type and number reactive group(s) present. It is knownthat different groups have different reactivities. For example, in thepresence of moisture, a silicon-bonded acetoxy group will usuallyhydrolyze more rapidly than a silicon-bonded alkoxy group when all otherconditions are the same. Furthermore, even the same type of curablegroup can have different reactivities depending on the number of thosecurable groups bonded to a particular silicon atom. For example, if apolydiorganosiloxane has three silicon-bonded alkoxy groups bonded toone silicon atom on a chain end, then the first alkoxy group isgenerally most reactive (reacts most quickly), but after the firstalkoxy group reacts, it takes a longer time for the second alkoxy groupbonded to the same silicon atom to react, and even longer for the third.Therefore, there is a continuing need to prepare clustered functionalpolyorganosiloxanes having more of the “most” reactive groups permolecular terminus.

The synthesis of ‘dumb-bell’ silicone polymers, in which long polymerchains are capped with cyclic, linear and star-shaped species having oneor more organo-functional groups has been disclosed. Such polymers havebeen described which can undergo a number of cure chemistries, e.g.,epoxy (glycidyl, alkylepoxy, and cycloaliphatic epoxy), methacrylate,acrylate, urethanes, alkoxy, or addition.

It is desirable to make multifunctional end blocked polymers (clusteredfunctional polyorganosiloxanes) in which the curable groups areclustered at the ends/termini of the polymers. The combination ofclustered functional groups with nonfunctional polymer chains separatingthem in the ‘dumb-bell’ silicone polymers may provide higher physicalproperties with the minimum drop in cure rate. This approach has beendemonstrated for ‘dumb-bell’ silicone polymers in which the curablegroups are the same (for example, all curable groups clustered at thepolymer chain ends may be either epoxy or alkoxy). This approach hasalso been demonstrated for so called ‘multiple cure’ systems in whichthe curable groups differ, for example, all curable groups clustered atthe polymer terminals may be a combination of epoxy and alkoxy groups.

Thermally conductive silcone compositions including these clusteredfunctional polyorganosiloxanes are utilized in bonding hybrid circuitsubstrates, power semiconductor components and devices to heat sinks aswell as for use in other bonding applications where flexibility andthermal conductivity are major concerns. The low viscosity versions ofthese thermally conductive silcone compositions are ideal for use asthermally conductive potting materials for transformers, power supplies,coils and other electronic devices that require improved thermaldissipation.

In order to make these curable polyorganosiloxane compositions moredispensable for application purposes, it is often necessary or desirableto reduce their viscosities through the use of viscosity reducingpolymers, sometimes referred to as reactive diluents. Such reactivediluents should be compatible with the curable polyorganosiloxanecompositions and function to reduce viscosity without adverselyaffecting properties of the composition both prior to application (suchas storage stability) and subsequent to application (including curingrates and cured physical properties of the compositions).

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a method, hereinafter referred to as anIn Situ method, for forming a thermally conductive thermal radical curesilicone composition that comprises (I) a thermally conductive clusteredfunctional polyorganopolysiloxane and (II) a radical initiator.

The method for forming a thermally conductive thermal radical curesilicone composition comprises (a) forming a thermally conductiveclustered functional polymer comprising the reaction product of areaction of a polyorganosiloxane having an average, per molecule, of atleast 2 aliphatically unsaturated organic groups; apolyorganohydrogensiloxane having an average of 4 to 15 silicon atomsper molecule; and a reactive species having, per molecule, at least 1aliphatically unsaturated organic group and 1 or more curable groups; inthe presence of a filler treating agent, a filler comprising a thermallyconductive filler, an isomer reducing agent, and a hydrosilylationcatalyst. The in situ method further comprises (b) blending thethermally conductive clustered functional polymer with a radicalinitiator.

This thermally conductive silicone composition formed by the In SituMethod offers many advantages over prior adhesive compositions due toits ability to cure by two distinct methods, namely moisture cure andthermal radical cure, without adversely affecting its mechanical andphysical properties. Thus, the adhesive may be used over a wider varietyof substrates, including plastic substrates and metal substrates.

The thermally conductive thermal radical cure silicone compositionformed by the In Situ Method are useful in composite articles ofmanufacture in which substrates are coated or bonded together with thecurable composition and cured. They can also be used in the preparationof various electrically conductive rubbers, electrically conductivetapes, electrically conductive adhesives, electrically conductive foams,and electrically conductive pressure sensitive adhesives; especiallywhere the rubber, tape, adhesive, or pressure sensitive adhesive, areelectrically conductive silicone rubbers, electrically conductivesilicone tapes, electrically conductive silicone adhesives, electricallyconductive silicone foams, and electrically conductive silicone pressuresensitive adhesives.

The thermally conductive thermal radical cure silicone compositionformed by the In Situ Method are useful in composite articles ofmanufacture in which substrates are coated or bonded together with thecurable composition and cured. The thermally conductive thermal radicalcure silicone composition can also be used to prepare thermal interfacematerials, thermally conductive rubbers, thermally conductive tapes,thermally conductive curable adhesives, thermally conductive foams, andthermally conductive pressure sensitive adhesives. They are especiallyuseful for preparing thermally conductive thermal radical cure adhesivecomposition used as die attachment adhesives, solder replacements, andthermally conductive coatings and gaskets. The thermally conductivethermal radical cure adhesive composition are especially useful forbonding electronic components to flexible or rigid substrates

These and other features of the invention will become apparent from aconsideration of the description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The articles ‘a’, ‘an’, and ‘the’ each refer to one or more, unlessotherwise indicated. All amounts, ratios, and percentages in thisapplication are by weight, unless otherwise indicated. All kinematicviscosities were measured at 25° C., unless otherwise indicated.

The present invention relates to a novel method, hereinafter referred toas the “In Situ Method”, for forming thermally conductive thermalradical cure silicone compositions that comprises (I) a thermallyconductive clustered functional polyorganopolysiloxane and (II) aradical initiator, as well as other optional components. In certainembodiments, the thermally conductive thermal radical cure siliconecompositions further includes (III) a silicone reactive diluent.

As will be discussed further below, the In Situ Method offers uniqueadvantages for producing thermally conductive thermal radical curesilicone compositions due to its ability to cure by two distinctmethods, namely moisture cure and thermal radical cure, withoutadversely affecting its mechanical and physical properties. Thus, theadhesive may be used over a wider variety of substrates, includingplastic substrates and metal substrates.

Component (I) is a thermally conductive clustered functionalpolyorganopolysiloxane that includes the following subcomponents:

(a) a polyorganosiloxane having an average, per molecule, of at least 2aliphatically unsaturated organic groups;

(b) a polyorganohydrogensiloxane having an average of 4 to 15 siliconatoms per molecule; and

(c) a reactive species having, per molecule, at least 1 aliphaticallyunsaturated organic group and 1 or more curable groups;

(d) a hydrosilylation catalyst;

(e) an isomer reducing agent;

(f) a filler comprising a thermally conductive filler;

(g) a filler treating agent, and

optional additional components.

Component (a) is a polyorganosiloxane having an average, per molecule,of at least 2 aliphatically unsaturated organic groups, which arecapable of undergoing a hydrosilylation reaction with a silicon bondedhydrogen atom of component (b). Component a) may have a linear orbranched structure. Alternatively, component (a) may have a linearstructure. Component (a) may be a combination comprising two or morepolyorganosiloxanes that differ in at least one of the followingproperties: structure, viscosity, degree of polymerization, andsequence.

Component (a) has a minimum average degree of polymerization (averageDP) of 100. Alternatively, average DP of component (a) may range from100 to 1000. The distribution DP of polyorganosiloxanes of component (a)can be bimodal. For example, component (a) may comprise one alkenylterminated polydiorganosiloxane with a DP of 60 and another alkenylterminated polydiorganosiloxane with a DP higher than 100, provided thataverage DP of the polydiorganosiloxanes ranges from 100 to 1000.However, suitable polyorganosiloxanes for use in component (a) have aminimum degree of polymerization (DP) of 10, provided thatpolyorganosiloxanes with DP less than 10 are combined withpolyorganosiloxanes having DP greater than 100. Suitablepolydiorganosiloxanes for component (a) are known in the art and arecommercially available. For example, Dow Corning® SFD-128 has DP rangingfrom 800 to 1000, Dow Corning® SFD-120 has DP ranging from 600 to 700,Dow Corning® 7038 has DP of 100, and Dow Corning® SFD-119 has DP of 150.All of these are vinyl-terminated polydimethylsiloxanes are commerciallyavailable from Dow Corning Corporation of Midland, Mich., USA. Whencomponent (a) has a bimodal distribution, the polyorganosiloxane withthe lower DP (low DP polyorganosiloxane) is present in a lower amountthan the polyorganosiloxane with the higher DP (high DPpolyorganosiloxane). For example, in a bimodal distribution, the ratioof low DP polyorganosiloxane/high DP polyorganosiloxane may range from10/90 to 25/75.

Component (a) is exemplified by polyorganosiloxanes of formula (I),formula (II), or a combination thereof. Formula (I) is R⁷ ₂R⁸SiO(R¹₂SiO)_(g)(R⁷R⁸SiO)_(h)SiR⁷ ₂R⁸, and formula (II) is R⁷ ₃SiO(R⁷₂SiO)_(i)(R⁷R⁸SiO)_(j)SiR⁷ ₃. In these formulae, each R⁷ isindependently a monovalent organic group free of aliphatic unsaturation,each R⁸ is independently an aliphatically unsaturated organic group,subscript g has an average value ranging from 2 to 1000, subscript h hasan average value ranging from 0 to 1000, subscript i has an averagevalue ranging from 0 to 1000, and subscript j has an average valueranging from 4 to 1000. In formulae (I) and (II), 10≦(g+h)≦1000 and10≦(i+j)≦1000.

Suitable monovalent organic groups for R⁷ include, but are not limitedto, monovalent hydrocarbon groups exemplified by alkyl such as methyl,ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkylsuch as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and2-phenylethyl. Each R⁸ is independently an aliphatically unsaturatedmonovalent organic group. R⁸ may be an aliphatically unsaturatedmonovalent hydrocarbon group exemplified by alkenyl groups such asvinyl, allyl, propenyl, and butenyl; and alkynyl groups such as ethynyland propynyl.

Component (a) may comprise a polydiorganosiloxane such as i)dimethylvinylsiloxy-terminated polydimethylsiloxane, ii)dimethylvinylsiloxy-terminatedpoly(dimethylsiloxane/methylvinylsiloxane), iii)dimethylvinylsiloxy-terminated polymethylvinylsiloxane, iv)trimethylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane),v) trimethylsiloxy-terminated polymethylvinylsiloxane, vi)dimethylvinylsiloxy-terminatedpoly(dimethylsiloxane/methylphenylsiloxane), vii)dimethylvinylsiloxy-terminated poly(dimethylsiloxane/diphenylsiloxane),viii) phenyl,methyl,vinyl-siloxy-terminated polydimethylsiloxane, ix)dimethylhexenylsiloxy-terminated polydimethylsiloxane, x)dimethylhexenylsiloxy-terminatedpoly(dimethylsiloxane/methylhexenylsiloxane), xi)dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane, xii)trimethylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane),or xiii) a combination thereof.

Component (b) is a polyorganohydrogensiloxane having an average of 4 to15 silicon atoms per molecule. Component (b) has an average of at least4 silicon bonded hydrogen atoms per aliphatically unsaturated organicgroup in component (a). Component (b) may be cyclic, branched, orlinear. Alternatively, component (b) may be cyclic. Component (b) may bea combination comprising two or more polyorganohydrogensiloxanes thatdiffer in at least one of the following properties: structure,viscosity, degree of polymerization, and sequence.

Component (b) may be a cyclic polyorganohydrogensiloxane having anaverage of 4 to 15 siloxane units per molecule. The cyclicpolyorganohydrogensiloxane may have formula (III), where formula (III)is (R⁹ ₂SiO_(2/2))_(k)(HR⁹SiO_(2/2))_(l), in which each R⁹ isindependently a monovalent organic group free of aliphatic unsaturation,subscript k has an average value ranging from 0 to 10, subscript I hasan average value ranging from 4 to 15, and a quantity (k+l) has a valueranging from 4 to 15, alternatively 4 to 12, alternatively 4 to 10,alternatively 4 to 6, and alternatively 5 to 6. Monovalent organicgroups suitable for R⁹ include, but are not limited to, monovalenthydrocarbon groups exemplified by alkyl such as methyl, ethyl, propyl,butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkyl such ascyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and2-phenylethyl.

Alternatively, component (b) may be a branchedpolyorganohydrogensiloxane. The branched polyorganohydrogensiloxane forcomponent (b) may have formula (IV), where formula (IV) is Si—(OSiR¹⁰₂)_(m)(OSiHR¹⁰)_(m), (OSiR¹⁰ ₃)_(n)(OSiR¹⁰ ₂H)_((4-n)), in which eachR¹⁰ is independently a monovalent organic group free of aliphaticunsaturation, subscript m has a value ranging from 0 to 10, subscript m′has a value ranging from 0 to 10, and subscript n has a value rangingfrom 0 to 1.

Alternatively, subscript m may be 0. When subscript m′ is 0, thensubscript n is also 0. Monovalent organic groups suitable for R¹⁰include, but are not limited to, monovalent hydrocarbon groupsexemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl,octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and arylsuch as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Alternatively, component (b) may be a linear polyorganohydrogensiloxanehaving an average of at least 4 silicon bonded hydrogen atoms permolecule. The linear polyorganohydrogensiloxane for component (b) mayhave a formula selected from (V), (VI), or a combination thereof, whereformula (V) is R¹¹ ₂HSiO(R¹¹ ₂SiO)_(o)(R¹¹HSiO)_(p)SiR¹¹ ₂H, formula(VI) is R¹¹ ₃SiO(R¹¹ ₂SiO)_(q)(R¹¹HSiO)_(r)SiR¹¹ ₃; where each R¹¹ isindependently a monovalent organic group free of aliphatic unsaturation,subscript o has an average value ranging from 0 to 12, subscript p hasan average value ranging from 2 to 12, subscript q has an average valueranging from 0 to 12, and subscript r has an average value ranging from4 to 12 where 4≦(o+p)≦13 and 4≦(q+r)≦13. Monovalent organic groupssuitable for R¹¹ include, but are not limited to, monovalent hydrocarbongroups exemplified by alkyl such as methyl, ethyl, propyl, butyl,pentyl, octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl;and aryl such as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Component (a) and component (b) may be present in amounts sufficient toprovide a weight percent of silicon bonded hydrogen atoms in component(b)/a weight percent of unsaturated organic groups in component (a)(commonly referred to as SiH_(b)/Vi_(a) ratio) ranging from 4/1 to 20/1,alternatively 4/1 to 10/1, and alternatively 5/1 to 20/1. Withoutwishing to be bound by theory, it is thought that if the SiH_(b)/Vi_(a)ratio is 30/1 or higher, the components may crosslink to form a productwith undesirable physical properties; and if the SiH_(b)/Vi_(a) ratio isless than 4/1, the product of the process may not have sufficientclustered functional groups to have fast enough cure speed, particularlyif a monofunctional reactive species (having one curable group permolecule) is used as component c).

Without wishing to be bound by theory, it is thought that using anexcess of silicon bonded hydrogen atoms in component (b), relative toaliphatically unsaturated organic groups in component (a), may reducethe possibilities of producing high homologs of the clustered functionalpolyorganosiloxanes, which tend to be insoluble in, and may reducestorage life of, a thermally conductive clustered functionalpolyorganopolysiloxane prepared by the process described herein. Theexcess of silicon bonded hydrogen atoms in component (b) may also resultin small (relatively low DP) thermally conductive clustered functionalpolyorganopolysiloxane, which may act as reactive diluents or viscositymodifiers and adhesion promoters. It is difficult to make these highlyfunctional small molecules in an industrial environment because theinhibiting nature of small highly functional silicone hydrides meanstemperatures above 50° C. are typically required to initiate thehydrosilylation process. This is then followed by a large exotherm,which can be dangerous in the presence of large volumes of solvent, orif careful monitoring of reagents is not used to control thetemperature. By simply changing the SiH_(b)/Vi_(a) ratio, these speciescan be made in a dilute solution of clustered functionalpolyorganosiloxane and filler, thereby significantly reducing gelationand chance of fire due to uncontrolled exothermic reaction.

Component c) is a reactive species. The reactive species may be anyspecies that can provide the curable groups in the thermally conductiveclustered functional polyorganopolysiloxane. The reactive species has anaverage, per molecule, of at least one aliphatically unsaturated organicgroup that is capable of undergoing an addition reaction with a siliconbonded hydrogen atom of component (b). Component c) further comprisesone or more radical curable groups per molecule. The radical curablegroups are functional (reactive) groups that render the clusteredfunctional polyorganosiloxane (prepared by the process described above)radiation curable. The radical curable groups on component c) may beselected from acrylate groups and methacrylate groups and combinationsthereof. Alternatively, the curable groups on component c) may beselected from acrylate, alkoxy, epoxy, methacrylate, and combinationsthereof.

For example, component c) may comprise a silane of formula (VIII), whereformula (VIII) is R¹² ₅siR¹³ _((3-s)); in which subscript s has a valueranging from 1 to 3, each R¹² is independently an aliphaticallyunsaturated organic group, and each R¹³ is independently selected froman organic group containing an acrylate group and a methacrylate group.

Alternatively, component c) may comprise an organic compound (which doesnot contain a silicon atom). The organic compound for component c) mayhave an average, per molecule, of 1 to 2 aliphatically unsaturatedorganic groups, such as alkenyl or alkynyl groups, and one or morereactive groups selected from an acrylate group and a methacrylategroup. Examples of suitable organic compounds for component c) include,but are not limited to, an allyl acrylate and allyl methacrylate (AMA);and combinations thereof.

The amount of component c) depends on various factors including thetype, amount, and SiH content of component (b) and the type of componentc) selected. However, the amount of component c) is sufficient to makeSiH_(tot)/Vi_(tot) range from 1/1 to 1/1.4, alternatively 1/1.2 to1.1/1. The ratio SiH_(tot)/Vi_(tot) means the weight percent of siliconbonded hydrogen atoms on component (b) and, if present component g) thechain extender and/or component h) the endcapper (described below),divided by the total weight percent of aliphatically unsaturated organicgroups on components (a) and c) combined.

Component d) is a hydrosilylation catalyst which accelerates thereaction of components (a), (b), and c). Component d) may be added in anamount sufficient to promote the reaction of components (a), (b), andc), and this amount may be, for example, sufficient to provide 0.1 partsper million (ppm) to 1000 ppm of platinum group metal, alternatively 1ppm to 500 ppm, alternatively 2 ppm to 200, alternatively 5 ppm to 20ppm, based on the combined weight of all components used in the process.

Suitable hydrosilylation catalysts are known in the art and commerciallyavailable. Component d) may comprise a platinum group metal selectedfrom platinum (Pt), rhodium, ruthenium, palladium, osmium or iridiummetal or organometallic compound thereof, or a combination thereof.Component d) is exemplified by compounds such as chloroplatinic acid,chloroplatinic acid hexahydrate, platinum dichloride, and complexes ofsaid compounds with low molecular weight organopolysiloxanes or platinumcompounds microencapsulated in a matrix or coreshell type structure.Complexes of platinum with low molecular weight organopolysiloxanesinclude 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes withplatinum. These complexes may be microencapsulated in a resin matrix.Alternatively, the catalyst may comprise1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum. Whenthe catalyst is a platinum complex with a low molecular weightorganopolysiloxane, the amount of catalyst may range from 0.04% to 0.4%based on the combined weight of the components used in the process.

Suitable hydrosilylation catalysts for component d) are described in,for example, U.S. Pat. Nos. 3,159,601; 3,220,972; 3,296,291; 3,419,593;3,516,946; 3,814,730; 3,989,668; 4,784,879; 5,036,117; and 5,175,325 andEP 0 347 895 B. Microencapsulated hydrosilylation catalysts and methodsof preparing them are known in the art, as exemplified in U.S. Pat. No.4,766,176; and U.S. Pat. No. 5,017,654.

Component (e) is an isomer reducing agent. In certain embodiments, theisomer reducing agent comprises a carboxylic acid compound. Thecarboxylic acid compound may comprise (1) carboxylic acid, (2) ananhydride of a carboxylic acid, (3) a carboxylic silyl ester, and/or (4)a substance that will produce the above-mentioned carboxylic acidcompounds (i.e., (1), (2), and/or (3)) through a reaction ordecomposition in the reaction of the method. It is to be appreciatedthat a mixture of one or more of these carboxylic acid compounds may beutilized as the isomer reducing agent. For example, a carboxylic silylester may be utilized in combination with an anhydride of a carboxylicacid as the isomer reducing agent. In addition, a mixture within one ormore types of carboxylic acid compounds may be utilized as the isomerreducing agent. For example, two different carboxylic silyl esters maybe utilized in concert, or two carboxylic silyl esters may be utilizedin concert with an anhydride of a carboxylic acid.

When the isomer reducing agent comprises (1) carboxylic acid, anycarboxylic acid having carboxyl groups may be utilized. Suitableexamples of carboxylic acids include saturated carboxylic acids,unsaturated carboxylic acids, monocarboxylic acids, and dicarboxylicacids. A saturated or unsaturated aliphatic hydrocarbon group, aromatichydrocarbon group, halogenated hydrocarbon group, hydrogen atom, or thelike is usually selected as the portion other than the carboxyl groupsin these carboxylic acids. Specific examples of suitable carboxylicacids include saturated monocarboxylic acids such as formic acid, aceticacid, propionic acid, n-butyric acid, isobutyric acid, hexanoic acid,cyclohexanoic acid, lauric acid, and stearic acid; saturateddicarboxylic acids such as oxalic acid and adipic acid; aromaticcarboxylic acids such as benzoic acid and para-phthalic acid; carboxylicacids in which the hydrogen atoms of the hydrocarbon groups of thesecarboxylic acids have been substituted with a halogen atom or anorganosilyl group, such as chloroacetic acid, dichloroacetic acid,trifluoroacetic acid, para-chlorobenzoic acid, and trimethylsilylaceticacid; unsaturated fatty acids such as acrylic acid, methacrylic acid,and oleic acid; and compounds having hydroxy groups, carbonyl groups, oramino groups in addition to carboxyl groups, namely, hydroxy acids suchas lactic acid, keto acids such as acetoacetic acid, aldehyde acids suchas glyoxylic acid, and amino acids such as glutamic acid.

When the isomer reducing agent comprises (2) an anhydride of carboxylicacid, suitable examples of anhydrides of carboxylic acids include aceticanhydride, propionic anhydride, and benzoic anhydride. These anhydridesof carboxylic acids may be obtained via a reaction or decomposition inthe reaction system include acetyl chloride, butyryl chloride, benzoylchloride, and other carboxylic acid halides, carboxylic acid metal saltssuch as zinc acetate and thallium acetate, and carboxylic esters thatare decomposed by light or heat, such as (2-nitrobenzyl) propionate.

In embodiments where the isomer reducing agent comprises (3) acarboxylic silyl ester, suitable examples of carboxylic silyl esters aretrialkylsilylated carboxylic acids, such as trimethylsilyl formate,trimethylsilyl acetate, triethylsilyl propionate, trimethylsilylbenzoate, and trimethylsilyl trifluoroacetate; and di-, tri-, ortetracarboxysilylates, such as dimethyldiacetoxysilane,diphenyldiacetoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane,vinyltriacetoxysilane, di-t-butoxydiacetoxysilane, and silicontetrabenzoate.

The isomer reducing agent is typically utilized in an amount rangingfrom 0.001 to 1 weight percent, alternatively from 0.01 to 0.1 weightpercent, based on the total weight of the thermally conductive clusteredfunctional polyorganopolysiloxane. Examples of commercially availablecarboxylic silyl esters suitable as the isomer reducing agent are DOWCORNING® ETS 900 or XIAMETER® OFS-1579 Silane, available from DowCorning Corporation of Midland, Mich.

The isomer reducing agent (e), added in a sufficient amount such as from0.001 to 1 weight percent as noted above, promotes the alpha-addition ofthe SiH groups of the polyorganosiloxane (b) to the aliphaticallyunsaturated group of the reactive species c) over the beta-addition ofthe SiH groups of the polyorganosiloxane (b) to the aliphaticallyunsaturated group of the reactive species c). The beta-position additionmay result in the subsequent further reaction of the polyorganosiloxaneto generate Si—OH and associated silicon hydroxide product (sometimesreferred to as D(Oz) and/or T(Oz) units). Without being bound by anytheory, it is believed that the generation of Si—OH hastens moisturecure of the thermally conductive clustered functionalpolyorganopolysiloxane. The relative amount of D(Oz) units generated,which correlate to the amount of beta-position addition of SiH groups ofthe polyorganosiloxane (b) to the aliphatically unsaturated group of thereactive species c), may be measured by NMR.

The thermally conductive clustered functional polyorganopolysiloxaneproduced in accordance with the present invention utilizing a sufficientamount of isomer reducing agent (e) results in a reduction, and incertain embodiments at least a 10% reduction, in the amount of D(Oz)units present in the formed thermally conductive clustered functionalpolyorganopolysiloxane, as measured by NMR, which corresponds to areduction, and in certain embodiments at least a 10% reduction in thebeta-addition of SiH groups of the polyorganosiloxane (b) to thealiphatically unsaturated group of the reactive species c).

The thermally conductive clustered functional polyorganopolysiloxanealso includes (f) a filler that includes a thermally conductive filler.In certain embodiments, in addition to thermally conductive filler, thefiller (f) may also comprise a reinforcing filler, an extending filler,or a combination thereof.

Thermally conductive filler may be both thermally conductive andelectrically conductive. Alternatively, thermally conductive filler maybe thermally conductive and electrically insulating. Thermallyconductive filler may be selected from the group consisting of aluminumnitride, aluminum oxide, aluminum trihydrate, barium titanate, berylliumoxide, boron nitride, carbon fibers, diamond, graphite, magnesiumhydroxide, magnesium oxide, metal particulate, onyx, silicon carbide,tungsten carbide, zinc oxide, and a combination thereof. Thermallyconductive filler may comprise a metallic filler, an inorganic filler, ameltable filler, or a combination thereof. Metallic fillers includeparticles of metals and particles of metals having layers on thesurfaces of the particles. These layers may be, for example, metalnitride layers or metal oxide layers on the surfaces of the particles.Suitable metallic fillers are exemplified by particles of metalsselected from the group consisting of aluminum, copper, gold, nickel,silver, and combinations thereof, and alternatively aluminum. Suitablemetallic fillers are further exemplified by particles of the metalslisted above having layers on their surfaces selected from the groupconsisting of aluminum nitride, aluminum oxide, copper oxide, nickeloxide, silver oxide, and combinations thereof. For example, the metallicfiller may comprise aluminum particles having aluminum oxide layers ontheir surfaces.

Inorganic fillers are exemplified by onyx; aluminum trihydrate, metaloxides such as aluminum oxide, beryllium oxide, magnesium oxide, andzinc oxide; nitrides such as aluminum nitride and boron nitride;carbides such as silicon carbide and tungsten carbide; and combinationsthereof. Alternatively, inorganic fillers are exemplified by aluminumoxide, zinc oxide, and combinations thereof. Meltable fillers maycomprise Bi, Ga, In, Sn, or an alloy thereof. The meltable filler mayoptionally further comprise Ag, Au, Cd, Cu, Pb, Sb, Zn, or a combinationthereof. Examples of suitable meltable fillers include Ga, In—Bi—Snalloys, Sn—In—Zn alloys, Sn—In—Ag alloys, Sn—Ag—Bi alloys, Sn—Bi—Cu—Agalloys, Sn—Ag—Cu—Sb alloys, Sn—Ag—Cu alloys, Sn—Ag alloys, Sn—Ag—Cu—Znalloys, and combinations thereof. The meltable filler may have a meltingpoint ranging from 50° C. to 250° C., alternatively 150° C. to 225° C.The meltable filler may be a eutectic alloy, a non-eutectic alloy, or apure metal. Meltable fillers are commercially available.

For example, meltable fillers may be obtained from Indium Corporation ofAmerica, Utica, N.Y., U.S.A.; Arconium, Providence, R.I., U.S.A.; andAIM Solder, Cranston, R.I., U.S.A. Aluminum fillers are commerciallyavailable, for example, from Toyal America, Inc. of Naperville, Ill.,U.S.A. and Valimet Inc., of Stockton, Calif., U.S.A. Silver filler iscommercially available from Metalor Technologies U.S.A. Corp. ofAttleboro, Mass., U.S.A. Silver flake filler is sold under the tradenameRA-127 by the American Chemet Corporation, Chicago, Ill.

Thermally conductive fillers are known in the art and commerciallyavailable, see for example, U.S. Pat. No. 6,169,142 (col. 4, lines7-33). For example, CB-A20S and Al-43-Me are aluminum oxide fillers ofdiffering particle sizes commercially available from Showa-Denko, DAW-45is aluminum oxide filler commercially available from Denka, and AA-04,AA-2, and AA18 are aluminum oxide fillers commercially available fromSumitomo Chemical Company. Zinc oxides, such as zinc oxides havingtrademarks KADOX® and XX®, are commercially available from ZincCorporation of America of Monaca, Pa., U.S.A.

The shape of thermally conductive filler particles is not specificallyrestricted, however, rounded or spherical particles may preventviscosity increase to an undesirable level upon high loading ofthermally conductive filler in the composition.

Thermally conductive filler may be a single thermally conductive filleror a combination of two or more thermally conductive fillers that differin at least one property such as particle shape, average particle size,particle size distribution, and type of filler. For example, it may bedesirable to use a combination of inorganic fillers, such as a firstaluminum oxide having a larger average particle size and a secondaluminum oxide having a smaller average particle size. Alternatively, itmay be desirable, for example, use a combination of an aluminum oxidehaving a larger average particle size with a zinc oxide having a smalleraverage particle size. Alternatively, it may be desirable to usecombinations of metallic fillers, such as a first aluminum having alarger average particle size and a second aluminum having a smalleraverage particle size. Alternatively, it may be desirable to usecombinations of metallic and inorganic fillers, such as a combination ofaluminum and aluminum oxide fillers; a combination of aluminum and zincoxide fillers; or a combination of aluminum, aluminum oxide, and zincoxide fillers. Use of a first filler having a larger average particlesize and a second filler having a smaller average particle size than thefirst filler may improve packing efficiency, may reduce viscosity, andmay enhance heat transfer.

The average particle size of thermally conductive filler will depend onvarious factors including the type of thermally conductive fillerselected and the exact amount added to the curable silicone composition,as well as the bondline thickness of the device in which the curedproduct of the composition will be used when the cured product will beused as a thermal interface material (TIM). However, thermallyconductive filler may have an average particle size ranging from 0.1micrometer to 80 micrometers, alternatively 0.1 micrometer to 50micrometers, and alternatively 0.1 micrometer to 10 micrometers.

The amount of thermally conductive filler as a part of (f) in thermallyconductive thermal radical cure silicone composition depends on variousfactors including the cure mechanism selected and the specific thermallyconductive filler selected. However, the amount of thermally conductivefiller as a part of (f) may range from 30 vol % to 80 vol %,alternatively 50 vol % to 75 vol % by volume of thermally conductivethermal radical cure adhesive composition. Without wishing to be boundby theory, it is thought that when the amount of thermally conductivefiller as a part of (f) is greater than 80 vol %, thermally conductivethermal radical cure silicone composition may crosslink to form a curedsilicone with insufficient dimensional integrity for some applications,and when the amount of thermally conductive filler as a part of (f) isless than 30%, the cured silicone prepared from thermally conductivethermal radical cure silicone composition may have insufficient thermalconductivity for TIM applications.

When alumina powder is used as thermally conductive filler, it ispreferably a mixture of a first spherical alumina filler and a secondspherical or irregularly shaped alumina powder having a different,preferably smaller average particle size. The amount of thermallyconductive filler (f) is typically added in an amount such thatthermally conductive thermal radical cure silicone composition has athermal conductivity of about 1 Watt per meter Kelvin or more. Thisimproves packing efficiency and can reduce the viscosity and enhanceheat transfer.

In certain embodiments, the thermally conductive thermal radical curesilicone composition may optionally further comprise a reinforcingfiller, which when present may be added in an amount ranging from 0.1%to 95%, alternatively 1% to 60%, based on the weight of all componentsin thermally conductive thermal radical cure adhesive composition. Theexact amount of the reinforcing filler depends on various factorsincluding the form of the cured product of the composition (e.g., gel orrubber) and whether any other fillers are added. Examples of suitablereinforcing fillers include chopped fiber such as chopped KEVLAR, and/orreinforcing silica fillers such as fume silica, silica aerogel, silicaxerogel, and precipitated silica. Fumed silicas are known in the art andcommercially available; e.g., fumed silica sold under the name CAB-O-SILby Cabot Corporation of Massachusetts, U.S.A.

The thermally conductive thermal radical cure silicone composition mayoptionally further comprise an extending filler in an amount rangingfrom 0.1% to 95%, alternatively 1 to 60%, and alternatively 1% to 20%,based on the weight of all components in thermally conductive thermalradical cure adhesive composition. Examples of extending fillers includecrushed quartz, aluminum oxide, magnesium oxide, calcium carbonate suchas precipitated calcium carbonate, zinc oxide, talc, diatomaceous earth,iron oxide, clays, mica, titanium dioxide, zirconia, sand, carbon black,graphite, or a combination thereof. Extending fillers are known in theart and commercially available; such as ground silica sold under thename MIN-U-SIL by U.S. Silica of Berkeley Springs, W. Va. Suitableprecipitated calcium carbonates included Winnofil® SPM from Solvay andUltrapflex® and Ultrapflex® 100 from SMI.

The filler (f) may also include a filler treating agent (g). The fillertreating agent (g) may be a treating agent, which is known in the art.The amount of filler treating agent (g) may vary depending on variousfactors including the type and amounts of thermally conductive fillersselected for component (f) and whether the filler (f) is treated withfiller treating agent in situ or pretreated before being combined.However, the components may comprise an amount ranging from 0.1% to 5%of filler treating agent (g), based on the weight of the filler (f) andthe type of the filler.

The filler treating agent (g) may comprise a silane such as analkoxysilane, an alkoxy-functional oligosiloxane, a cyclicpolyorganosiloxane, a hydroxyl-functional oligosiloxane such as adimethyl siloxane or methyl phenyl siloxane, a stearate, or a fattyacid. The alkoxysilane may have the formula: R¹⁰ _(p)Si(OR¹¹)_((4-p)),where subscript p is 1, 2, or 3; alternatively p is 3. Each R¹⁰ isindependently a monovalent organic group of 1 to 50 carbon atoms, suchas a monovalent hydrocarbon group of 1 to 50 carbon atoms, alternatively6 to 18 carbon atoms. Suitable monovalent hydrocarbon groups for R¹⁰ areexemplified by alkyl groups such as hexyl, octyl, dodecyl, tetradecyl,hexadecyl, and octadecyl; and aromatic groups such as benzyl, phenyl andphenylethyl. R¹⁰ can be a monovalent hydrocarbon group that is saturatedor unsaturated and branched or unbranched. Alternatively, R¹⁰ can be asaturated, unbranched, monovalent hydrocarbon group. Each R¹¹ may be asaturated hydrocarbon group of 1 to 4 carbon atoms, alternatively 1 to 2carbon atoms.

Alkoxysilane filler treating agents (g) are exemplified byhexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane,dodecyltrimethoxysilane, tetradecyltrimethoxysilane,phenyltrimethoxysilane, phenylethyltrimethoxysilane,octadecyltrimethoxysilane, octadecyltriethoxysilane, and a combinationthereof.

Alkoxy-functional oligosiloxanes can also be used as filler treatingagents (g). Alkoxy-functional oligosiloxanes and methods for theirpreparation are known in the art, see for example, EP 1 101 167 A2. Forexample, suitable alkoxy-functional oligosiloxanes include those of theformula (R¹⁴O)_(q)Si(OSiR¹² ₂R¹³)_((4-q)). In this formula, subscript qis 1, 2, or 3, alternatively q is 3. Each R¹² can be independentlyselected from saturated and unsaturated monovalent hydrocarbon groups of1 to 10 carbon atoms. Each R¹³ can be a saturated or unsaturatedmonovalent hydrocarbon group having at least 11 carbon atoms. Each R¹⁴can be an alkyl group.

Alternatively, the filler treating agent (g) can be any of theorganosilicon compounds typically used to treat silica fillers. Examplesof organosilicon compounds include, but are not limited to,organochlorosilanes such as methyltrichlorosilane,dimethyldichlorosilane, and trimethyl monochlorosilane; organosiloxanessuch as hydroxy-endblocked dimethylsiloxane oligomer,hexamethyldisiloxane, and tetramethyldivinyldisiloxane; organosilazanessuch as hexamethyldisilazane and hexamethylcyclotrisilazane; andorganoalkoxysilanes such as methyltrimethoxysilane,vinyltrimethoxysilane, vinyltriethoxysilane,3-glycidoxypropyltrimethoxysilane, and3-methacryloxypropyltrimethoxysilane. Examples of stearates includecalcium stearate. Examples of fatty acids include stearic acid, oleicacid, palmitic acid, tallow, coconut oil, and combinations thereof.Examples of filler treating agents and methods for their use aredisclosed in, for example, EP 1 101 167 A2 and U.S. Pat. Nos. 5,051,455,5,053,442, and 6,169,142 (col. 4, line 42 to col. 5, line 2).

Filler treating agents (g) may include alkoxysilyl functionalalkylmethyl polysiloxanes (e.g., partial hydrolysis condensate of R²²_(w)R²³ _(x)Si(OR²⁴)_((4-w-x)) or cohydrolysis condensates or mixtures),or similar materials where the hydrolyzable group may comprise silazane,acyloxy or oximo. In all of these, a group tethered to Si, such as R²²in the formula above, is a long chain unsaturated monovalent hydrocarbonor monovalent aromatic-functional hydrocarbon. Each R²³ is independentlya monovalent hydrocarbon group, and each R²⁴ is independently amonovalent hydrocarbon group of 1 to 4 carbon atoms. In the formulaabove, subscript w is 1, 2, or 3 and subscript x is 0, 1, or 2, with theproviso that the sum (w+x) is 1, 2, or 3. One skilled in the art wouldrecognize that the alkoxysilanes and mercapto-functional compoundsdescribed as adhesion promoters for component (IX)(see below) mayalternatively be used, in addition to or instead of, filler treatingagents (g) for the filler (f). One skilled in the art could optimize aspecific treatment to aid dispersion of the filler without undueexperimentation.

Other filler treating agents (g) include alkenyl functionalpolyorganosiloxanes. Suitable alkenyl functional polyorganosiloxanesinclude, but are not limited to:

where subscript q has a value up to 1,500. Other treating agents includemono-endcapped alkoxy functional polydiorganosiloxanes, i.e.,polydiorganosiloxanes having an alkoxy group at one end. Such treatingagents are exemplified by the formula: R²⁵R²⁶ ₂SiO(R²⁶₂SiO)_(u)Si(OR²⁷)₃, where subscript u has a value of 0 to 100,alternatively 1 to 50, alternatively 1 to 10, and alternatively 3 to 6.Each R²⁵ is independently selected from an alkyl group, such as Me, Et,Pr, Bu, hexyl, and octyl; and an alkenyl group, such as Vi, allyl,butenyl, and hexenyl. Each R²⁶ is independently an alkyl group such asMe, Et, Pr, Bu, hexyl, and octyl. Each R²⁷ is independently an alkylgroup such as Me, Et, Pr, and Bu. Alternatively, each R²⁵, each R²⁶, andeach R²⁷ is Me. Alternatively, each R²⁵ is a vinyl group (Vi).Alternatively, each R²⁶ and each R²⁷ is methyl (Me).

Alternatively, a polyorganosiloxane capable of hydrogen bonding isuseful as a filler treating agent (g). This strategy to treating thesurface of a thermally conductive filler takes advantage of multiplehydrogen bonds, either clustered or dispersed or both, as the means totether the compatibilization moiety to the filler surface. Thepolyorganosiloxane capable of hydrogen bonding has an average, permolecule, of at least one silicon-bonded group capable of hydrogenbonding. The group may be selected from: an organic group havingmultiple hydroxyl functionalities or an organic group having at leastone amino functional group. The polyorganosiloxane capable of hydrogenbonding means that hydrogen bonding is the primary mode of attachmentfor the polyorganosiloxane to thermally conductive filler. Thepolyorganosiloxane may be incapable of forming covalent bonds withthermally conductive filler. The polyorganosiloxane capable of hydrogenbonding may be selected from the group consisting of asaccharide-siloxane polymer, an amino-functional polyorganosiloxane, anda combination thereof. Alternatively, the polyorganosiloxane capable ofhydrogen bonding may be a saccharide-siloxane polymer.

Component (II) is a radical initiator. The radical initiator may be athermal radical initiator. Thermal radical initiators include, but arenot limited to, dicumyl peroxide, n-butyl 4,4′-bis(butylperoxy)valerate,1,1-bis(t-butylperoxy)-3,3,5 trimethyl cyclohexane, di-t-butyl peroxideand 2,5-di-(t-butylperoxy)-2,5 dimethyl hexane,1,1-bis(tert-amylperoxy)cyclohexane (Luperox® 531 M80);2,2-bis(tert-butylperoxy)butane; 2,4-pentanedione peroxide (Luperox®224), 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane (Luperox® 101),2,5-di(tert-butylperoxy)-2,5-dimethyl-3-hexyne; 2-butanone peroxide,benzoyl peroxide, cumene hydroperoxide, di-tert-amyl peroxide (Luperox®DTA®), lauroyl peroxide (Luperox® LP), tert-butyl hydroperoxide;tert-butyl peracetate; tert-butyl peroxybenzoate; tert-butylperoxy2-ethylhexyl carbonate; di(2,4-dichlorobenzoyl) peroxide;dichlorobenzoylperoxide (available as Varox® DCBP from R. T. VanderbiltCompany, Inc. of Norwalk, Conn., USA);di(tert-butylperoxyisopropyl)benzene, di(4-methylbenzoyl) peroxide,butyl 4,4-di(tert-butylperoxy)valerate,3,3,5,7,7-pentamethyl-1,2,4-trioxepane; tert-butylperoxy-3,5,5-trimethylhexanoate; tert-butyl cumyl peroxide;di(4-tert-butylcyclohexyl) peroxydicarbonate (available as Perkadox 16);dicetyl peroxydicarbonate; dimyristyl peroxydicarbonate;2,3-dimethyl-2,3-diphenylbutane, dioctanoyl peroxide; tert-butylperoxy2-ethylhexyl carbonate; tert-amyl peroxy-2-ethylhexanoate, tert-amylperoxypivalate; and combinations thereof.

Examples of such thermal radical initiators (II) are commerciallyavailable under the following trade names: Luperox® sold by Arkema, Inc.of Philadelphia, Pa., U.S.A.; Trigonox and Perkadox sold by Akzo NobelPolymer Chemicals LLC of Chicago, Ill., U.S.A., VAZO sold by E.I. duPontdeNemours and Co. of Wilmington, Del., USA; VAROX® sold by R.T.Vanderbilt Company, Inc. of Norwalk, Conn., U.S.A.; and Norox sold bySyrgis Performance Initiators, Inc. of Helena, Ark., U.S.A.

Alternatively, the radical initiator (II) may comprise a redox reagentas an initiator for radical polymerization. The reagent may be acombination of peroxide and an amine or a transition metal chelate. Theredox reagent is exemplified by, but not limited to, diacyl peroxidessuch as benzoyl peroxide and acetyl peroxide; hydroperoxides such ascumene hydroperoxide and t-butyl hydroperoxide; ketone peroxides such asmethyl ethyl ketone peroxide and cyclohexanone peroxide; dialkylperoxides such as dicumyl peroxide and ti-t-butyl peroxide; peroxyesters such as t-butyl peroxy acetate; and combinations of thioglyceroland pyrazoles and/or pyrazolones. Alternatively, the redox reagent maybe exemplified by dimethylaniline, 3,5-dimethylpyrazole, thioglycerol;and combinations thereof. Examples of suitable redox reagent initiatorsare known in the art and are exemplified as in U.S. Pat. No. 5,459,206.Other suitable peroxides are known in the art and are commerciallyavailable such as lauroyl peroxide (Luperox® LP from Arkema),dichlorobenzoylperoxide (Varox® DCBP from R. T. Vanderbilt Company,Inc.) and 6N tert-butyl hydroperoxide.

The concentration of the radical initiator (I) may range from 0.01% to15%, alternatively from 0.1% to 5%, and alternatively 0.1% to 2%, basedon the weight of the thermally conductive clustered functionalpolyorganosiloxane (I).

Thermally conductive thermally radical cure adhesive composition mayoptionally comprise one or more additional components. The additionalcomponents are exemplified by (III) a silicone diluent, (III) aclustered functional polyorganosiloxane; (V) a moisture cure initiator,(VI) a crosslinker, (VII) a moisture cure polymer, (VIII) a solvent,(IX) an adhesion promoter, (X) a colorant, (XI) a reactive diluent,(XII) a corrosion inhibitor, (XIII) a polymerization inhibitor, and(XIV) an acid acceptor, and a combination thereof.

Optional Component (III) is a silicone reactive diluent. The siliconereactive diluent (III) aids in dispensing of the curable siliconecomposition by reducing the viscosity of the curable siliconecomposition to make it more flowable.

In certain embodiments, the amount of silicone reactive diluent (III)utilized ranges from 20 to 90 weight percent, alternatively from 40 to70 weight percent, alternatively from 55 to 80 weight percent,alternatively from 55 to 75 weight percent, alternatively 70 weightpercent, based on the total silicone matrix weight of thermallyconductive thermal radical cure adhesive composition.

The silicone reactive diluent (III) may be a monofunctional siliconereactive diluent, a difunctional silicone reactive diluent, apolyfunctional silicone reactive diluent, or a combination thereof. Thesilicone reactive diluent selected will depend on various factorsincluding the curable groups. However, examples of suitable siliconereactive diluents include an acrylate, an anhydride such as a maleicanhydride or methacrylic anhydride, an epoxy such as a monofunctionalepoxy compound, a methacrylate such as glycidyl methacrylate, anoxetane, a vinyl acetate, a vinyl ester, a vinyl ether, a fluoro alkylvinyl ether, a vinyl pyrrolidone such as N-vinyl pyrrolidone, a styrene,or a combination thereof.

In certain embodiments, the silicone reactive diluent (III) may beformed in a first embodiment as the reaction product of a reaction of:

a) a polyorganohydrogensiloxane having an average of 10 to 200 siliconatoms per molecule; and

b) a reactive species having, per molecule, at least 1 aliphaticallyunsaturated organic group and 1 or more curable groups;

in the presence of c) an isomer reducing agent and d) a hydrosilylationcatalyst and e) inhibitor for hydrosilylation catalyst.

In certain other embodiments, additional optional components may also beincluded in the silicone reactive diluent (III) of the first embodiment.

Component a) of the silicone reactive diluent (III) in the firstembodiment is a polyorganohydrogensiloxane having an average of 10 to200 silicon atoms per molecule. Component a) may be branched or linear.Component a) may be monofunctional (i.e., includes one silicon-bondedhydrogen atom), a difunctional (i.e., includes two silicon-bondedhydrogen atoms), a polyfunctional (i.e., includes more than twosilicon-bonded hydrogen atoms), or a combination thereof. Component a)may be a combination comprising two or more polyorganohydrogensiloxaneseach having an average of 10 to 200 silicon atoms per molecule thatdiffer in at least one of the following properties: structure,viscosity, degree of polymerization, and sequence.

In certain embodiments, component a) may be a polydiorganosiloxaneterminated at both ends with hydrogen atoms. One exemplarypolydiorganosiloxane terminated at both ends with hydrogen atoms mayhave the formula HR₂Si—(R₂SiO)_(a)—SiR₂H, where each R is independentlya monovalent hydrocarbon group exemplified by alkyl such as methyl,ethyl, propyl, butyl, pentyl, and hexyl; and aryl such as phenyl, tolyl,xylyl, and benzyl. Subscript a has an average value ranging from 0 to400, alternatively 10 to 200.

Alternatively, component a) may be a branchedpolyorganohydrogensiloxane. The branched polyorganohydrogensiloxane forcomponent b) may have the formula Si—(OSiR² ₂)_(b)(OSiHR²)_(b′)(OSiR²₃)_(c)(OSiR² ₂H)_((4-c)), in which each R² is independently a monovalentorganic group free of aliphatic unsaturation, subscript b has a valueranging from 0 to 10, subscript b′ has a value ranging from 0 to 10, andsubscript c has a value ranging from 0 to 1.

Alternatively, subscript b may be 0. When subscript b′ is 0, thensubscript c is also 0. Monovalent organic groups suitable for R²include, but are not limited to, monovalent hydrocarbon groupsexemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl,octyl, undecyl, and octadecyl; cycloalkyl such as cyclohexyl; and arylsuch as phenyl, tolyl, xylyl, benzyl, and 2-phenylethyl.

Component b) of the silicone reactive diluent (III) in the firstembodiment is a reactive species. The reactive species b) may be anyspecies that can provide the curable groups in the silicone reactivediluent. The reactive species has an average, per molecule, of at leastone aliphatically unsaturated organic group that is capable ofundergoing an addition reaction with a silicon bonded hydrogen atom ofcomponent a). Component b) further comprises one or more radical curablegroups per molecule. The radical curable groups are functional(reactive) groups that render the silicone reactive diluent radiationcurable. The radical curable groups on component b) may be selected fromacrylate groups and methacrylate groups and combinations thereof.

For example, in certain embodiments, component b) may comprise a silaneof formula R³ _(d)SiR⁴ _((3-d)); in which subscript d has a valueranging from 1 to 3, each R³ is independently an aliphaticallyunsaturated organic group, and each R⁴ is independently selected from anorganic group containing an acrylate group and a methacrylate group.

Alternatively, component b) may comprise an organic compound (which doesnot contain a silicon atom). The organic compound for component b) mayhave an average, per molecule, of 1 to 2 aliphatically unsaturatedorganic groups, such as alkenyl or alkynyl groups, and one or morereactive groups selected from an acrylate group and a methacrylategroup. Examples of suitable organic compounds for component b) include,but are not limited to, allyl acrylate and allyl methacrylate (AMA), andcombinations thereof.

The amount of component b) depends on various factors including thetype, amount, and SiH content of component a) and the type of componentb) selected. However, the amount of component b) is sufficient to makeSiH_(tot)/Vi_(tot) range from 1/1 to 1/1.4, alternatively 1/1.2 to1.1/1. The ratio SiH_(tot)/Vi_(tot) means the weight percent of totalamount of silicon bonded hydrogen atoms on component b) divided by thetotal weight percent of aliphatically unsaturated organic groups oncomponent a).

Component (c) of the silicone reactive diluent (III) in the firstembodiment is an isomer reducing agent. In certain embodiments, theisomer reducing agent comprises a carboxylic acid compound. Thecarboxylic acid compound may comprise (1) carboxylic acid, (2) ananhydride of a carboxylic acid, (3) a carboxylic silyl ester, and/or (4)a substance that will produce the above-mentioned carboxylic acidcompounds (i.e., (1), (2), and/or (3)) through a reaction ordecomposition in the reaction of the method. It is to be appreciatedthat a mixture of one or more of these carboxylic acid compounds may beutilized as the isomer reducing agent. For example, a carboxylic silylester may be utilized in combination with an anhydride of a carboxylicacid as the isomer reducing agent. In addition, a mixture within one ormore types of carboxylic acid compounds may be utilized as the isomerreducing agent. For example, two different carboxylic silyl esters maybe utilized in concert, or two carboxylic silyl esters may be utilizedin concert with an anhydride of a carboxylic acid.

When the isomer reducing agent comprises (1) carboxylic acid, anycarboxylic acid having carboxyl groups may be utilized. Suitableexamples of carboxylic acids include saturated carboxylic acids,unsaturated carboxylic acids, monocarboxylic acids, and dicarboxylicacids. A saturated or unsaturated aliphatic hydrocarbon group, aromatichydrocarbon group, halogenated hydrocarbon group, hydrogen atom, or thelike is usually selected as the portion other than the carboxyl groupsin these carboxylic acids. Specific examples of suitable carboxylicacids include saturated monocarboxylic acids such as formic acid, aceticacid, propionic acid, n-butyric acid, isobutyric acid, hexanoic acid,cyclohexanoic acid, lauric acid, and stearic acid; saturateddicarboxylic acids such as oxalic acid and adipic acid; aromaticcarboxylic acids such as benzoic acid and para-phthalic acid; carboxylicacids in which the hydrogen atoms of the hydrocarbon groups of thesecarboxylic acids have been substituted with a halogen atom or anorganosilyl group, such as chloroacetic acid, dichloroacetic acid,trifluoroacetic acid, para-chlorobenzoic acid, and trimethylsilylaceticacid; unsaturated fatty acids such as acrylic acid, methacrylic acid,and oleic acid; and compounds having hydroxy groups, carbonyl groups, oramino groups in addition to carboxyl groups, namely, hydroxy acids suchas lactic acid, keto acids such as acetoacetic acid, aldehyde acids suchas glyoxylic acid, and amino acids such as glutamic acid.

When the isomer reducing agent comprises (2) an anhydride of carboxylicacid, suitable examples of anhydrides of carboxylic acids include aceticanhydride, propionic anhydride, and benzoic anhydride. These anhydridesof carboxylic acids may be obtained via a reaction or decomposition inthe reaction system include acetyl chloride, butyryl chloride, benzoylchloride, and other carboxylic acid halides, carboxylic acid metal saltssuch as zinc acetate and thallium acetate, and carboxylic esters thatare decomposed by light or heat, such as (2-nitrobenzyl) propionate.

In embodiments where the isomer reducing agent comprises (3) acarboxylic silyl ester, suitable examples of carboxylic silyl esters aretrialkylsilylated carboxylic acids, such as trimethylsilyl formate,trimethylsilyl acetate, triethylsilyl propionate, trimethylsilylbenzoate, and trimethylsilyl trifluoroacetate; and di-, tri-, ortetracarboxysilylates, such as dimethyldiacetoxysilane,diphenyldiacetoxysilane, methyltriacetoxysilane, ethyltriacetoxysilane,vinyltriacetoxysilane, di-t-butoxydiacetoxysilane, and silicontetrabenzoate.

The isomer reducing agent is typically utilized in an amount rangingfrom 0.001 to 1 weight percent, alternatively from 0.01 to 0.1 weightpercent, based on the total weight of the formed silicone reactivediluent. Examples of commercially available carboxylic silyl esterssuitable as the isomer reducing agent are DOW CORNING® ETS 900 orXIAMETER® OFS-1579 Silane, available from Dow Corning Corporation ofMidland, Mich.

The isomer reducing agent (c), added in a sufficient amount such as from0.001 to 1 weight percent as noted above, promotes the alpha-addition ofthe SiH groups of the polydiorganosiloxane (a) to the aliphaticallyunsaturated group of the reactive species b) over the beta-addition ofthe SiH groups of the polydiorganosiloxane (a) to the aliphaticallyunsaturated group of the reactive species b). The beta-position additionmay result in the subsequent further reaction of the polyorganosiloxaneto generate Si—OH and associated silicon hydroxide product (sometimesreferred to as D(Oz) and/or T(Oz) units). Without being bound by anytheory, it is believed that the generation of Si—OH hastens moisturecure of the polydiorganosiloxanes of the silicone reactive diluent(III). The relative amount of D(Oz) units generated, which correlate tothe amount of beta-position addition of SiH groups of thepolyorganosiloxane (ii) to the aliphatically unsaturated group of thereactive species (c), may be measured by NMR.

Component d) of the silicone reactive diluent (III) in the firstembodiment is a hydrosilylation catalyst which accelerates the reactionof components a) and b). Component d) may be added in an amountsufficient to promote the reaction of components a) and b), and thisamount may be, for example, sufficient to provide 0.1 parts per million(ppm) to 1000 ppm of platinum group metal, alternatively 1 ppm to 500ppm, alternatively 2 ppm to 200, alternatively 5 ppm to 150 ppm, basedon the combined weight of all components used in the process.

Suitable hydrosilylation catalysts are known in the art and commerciallyavailable. Component d) may comprise a platinum group metal selectedfrom platinum (Pt), rhodium, ruthenium, palladium, osmium or iridiummetal or organometallic compound thereof, or a combination thereof.Component d) is exemplified by compounds such as chloroplatinic acid,chloroplatinic acid hexahydrate, platinum dichloride, and complexes ofsaid compounds with low molecular weight organopolysiloxanes or platinumcompounds microencapsulated in a matrix or coreshell type structure.Complexes of platinum with low molecular weight organopolysiloxanesinclude 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complexes withplatinum. These complexes may be microencapsulated in a resin matrix.Alternatively, the catalyst may comprise1,3-diethenyl-1,1,3,3-tetramethyldisiloxane complex with platinum. Whenthe catalyst is a platinum complex with a low molecular weightorganopolysiloxane, the amount of catalyst may range from 0.04% to 0.4%based on the combined weight of the components used in the process.

Suitable hydrosilylation catalysts for component d) are described in,for example, U.S. Pat. Nos. 3,159,601; 3,220,972; 3,296,291; 3,419,593;3,516,946; 3,814,730; 3,989,668; 4,784,879; 5,036,117; and 5,175,325 andEP 0 347 895 B. Microencapsulated hydrosilylation catalysts and methodsof preparing them are known in the art, as exemplified in U.S. Pat. No.4,766,176; and U.S. Pat. No. 5,017,654.

Component e) of the silicone reactive diluent (III) in the firstembodiment is a catalyst inhibitor, which is added to deactivatecomponent d) (the hydrosilylation catalyst) and stabilize the formedsilicone reactive diluent. Some examples of suitable catalyst inhibitorsinclude ethylenically or aromatically unsaturated amides, acetyleniccompounds such as 2-ethynyl-isopropanol, 2-ethynyl-butane-2-ol,2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, 3,5-dimethyl-1-hexyn-3-ol,1-ethynyl-1-cyclohexanol, 1,5-hexadiene, 1,6-heptadiene;3,5-dimethyl-1-hexen-1-yne; 3-ethyl-3-buten-1-yne or3-phenyl-3-buten-1-yne; ethylenically unsaturated isocyanates; silylatedacetylenic alcohols exemplified by trimethyl(3,5-dimethyl-1-hexyn-3-oxy)silane,dimethyl-bis-(3-methyl-1-butyn-oxy)silane,methylvinylbis(3-methyl-1-butyn-3-oxy)silane, and((1,1-dimethyl-2-propynyl)oxy)trimethylsilane; unsaturated hydrocarbondiesters; conjugated ene-ynes exemplified by 2-isobutyl-1-butene-3-yne,3,5-dimethyl-3-hexene-1-yne, 3-methyl-3-pentene-1-yne,3-methyl-3-hexene-1-yne, 1-ethynylcyclohexene, 3-ethyl-3-butene-1-yne,and 3-phenyl-3-butene-1-yne; olefinic siloxanes such as1,3-divinyltetramethyldisiloxane, 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane, or 1,3-divinyl-1,3-diphenyldimethyldisiloxane;1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane; a mixture of aconjugated ene-yne as described above and an olefinic siloxane asdescribed above; hydroperoxides; nitriles and diaziridines; unsaturatedcarboxylic esters exemplified by diallyl maleate, dimethyl maleate,diethyl fumarate, diallyl fumarate, andbis-2-methoxy-1-methylethylmaleate, mono-octylmaleate,mono-isooctylmaleate, mono-allyl maleate, mono-methyl maleate,mono-ethyl fumarate, mono-allyl fumarate, and2-methoxy-1-methylethylmaleate; fumarates such as diethylfumarate;fumarate/alcohol mixtures wherein the alcohol is benzyl alcohol or1-octanol and ethenyl cyclohexyl-1-ol; a nitrogen-containing compoundsuch as tributylamine, tetramethylethylenediamine, benzotriazole; asimilar phosphorus-containing compound such as triphenylphosphine; asulphur-containing compound; a hydroperoxy compound; or a combinationthereof.

The inhibitors are used in an amount effective to deactivate componentd) the hydrosilylation catalyst. The amount will vary depending on thetype and amount of catalyst and the type of inhibitor selected, however,the amount may range from 0.001 to 3 parts by weight, and alternativelyfrom 0.01 to 1 part by weight per 100 parts by weight of component a).

In addition to Components a)-e), other optional components may beutilized in forming the silicone reactive diluent (III) of the firstembodiment. For example, in certain embodiments, the silicone reactivediluent may further include f) a polymerization inhibitor and g) anendcapper.

Optional component f) of the silicone reactive diluent (III) in thefirst embodiment is a polymerization inhibitor. The unsaturated groups(e.g., methacrylate, acrylate, vinyl or allyl) can autopolymerize viaunwanted radical process. These radical processes can be mitigated bythe addition of polymerization inhibitors. Examples of suitablepolymerization inhibitors for acrylate and methacrylate curable groupsinclude, but are not limited to:2,6,-Di-tert-butyl-4-(dimethylaminomethyl)phenol (DBAP), hydroquinone(HQ); 4-methoxyphenol (MEHQ); 4-ethoxyphenol; 4-propoxyphenol;4-butoxyphenol; 4-heptoxyphenol; butylated hydroxytoluene (BHT);hydroquinone monobenzylether; 1,2-dihydroxybenzene; 2-methoxyphenol;2,5-dichlorohydroquinone; 2,5-di-tert-butylhydroquinone;2-acetylhydroquinone; hydroquinone monobenzoate; 1,4-dimercaptobenzene;1,2-dimercaptobenzene; 2,3,5-trimethylhydroquinone; 4-aminophenol;2-aminophenol; 2-N, N-dimethylaminophenol; 2-mercaptophenol;4-mercaptophenol; catechol monobutylether; 4-ethylaminophenol;2,3-dihydroxyacetophenone; pyrogallol-1,2-dimethylether;2-methylthiophenol; t-butyl catechol; di-tert-butylnitroxide;di-tert-amylnitroxide; 2,2,6,6-tetramethyl-piperidinyloxy;4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;4-oxo-2,2,6,6-tetramethyl-piperidinyloxy;4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy;4-amino-2,2,6,6-tetramethyl-piperidinyloxy;4-ethanoloxy-2,2,6,6-tetramethyl-piperidinyloxy;2,2,5,5-tetramethyl-pyrrolidinyloxy;3-amino-2,2,5,5-tetramethyl-pyrrolidinyloxy;2,2,5,5-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy;2,2,5,5-tetramethyl-3-pyrrolinyl-1-oxy-3-carboxylic acid;2,2,3,3,5,5,6,6-octamethyl-1,4-diazacyclohexyl-1,4-dioxy; salts of4-nitrosophenolate; 2-nitrosophenol; 4-nitrosophenol; copperdimethyldithiocarbamate; copper diethyldithiocarbamate; copperdibutyldithiocarbamate; copper salicylate; methylene blue; iron;phenothiazine (PTZ); 3-oxophenothiazine; 5-oxophenothiazine;phenothiazine dimer; 1,4-benzenediamine;N-(1,4-dimethylpentyl)-N′-phenyl-1,4-benzenediamine;N-(1,3-dimethylbutyl)-N′-phenyl-1,4-benzenediamine;N-nitrosophenylhydroxylamine and salts thereof; nitric oxide;nitrobenzene; p-benzoquinone; pentaerythrityltetrakis(3-laurylthiopropionate); dilauryl thiodipropionate; distearyllthiodipropionate; ditridecyl thiodipropionate; tetrakis[methylene3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;N,N′-hexamethyl (3,5-di-tertbutyl-4-hydroxyhydrocinnamamide);iso-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;2,2′-ethylidenebis-(4,6-di-tert-butylphenol);1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene;4,6-bis(octylthiomethyl)-o-cresol; triethyleneglycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate;tris-(3,5-di-tert-butylhydroxybenzyl) isocyanurate;tris(2,4-di-tert-butylphenyl) phosphate; distearyl pentaerythritoldiphosphite; bis(2,4-di-tert-butyl phenyl)pentaerythritol diphosphite;2,5-di-tert-amyl-hydroquinone; or isomers thereof; combinations of twoor more thereof; or combinations of one or more of the above withmolecular oxygen. When present, the polymerization inhibitor may beadded to the curable silicone composition in an amount ranging from 100ppm to 4,000 ppm.

Optional component g) of the silicone reactive diluent (III) in thefirst embodiment is an endcapper. The endcapper may be apolydiorganosiloxane having one hydrogen atom per molecule. An exemplaryendcapper may have the formula R⁵ ₃Si—(R⁵ ₂SiO)_(e)—SiR⁵ ₂H. In thisformula, each R⁵ is independently a monovalent hydrocarbon groupexemplified by alkyl such as methyl, ethyl, propyl, butyl, pentyl, andhexyl; and aryl such as phenyl, tolyl, xylyl and benzyl; and subscript ehas a value ranging from 0 to 10, alternatively 1 to 10, andalternatively 1. Another exemplary endcapper may have the formula R⁶₃Si—(R⁶ ₂SiO)_(f)—(HR⁶SiO)—SiR⁶ ₃. In this formula, each R⁶ isindependently a monovalent hydrocarbon group exemplified by alkyl suchas methyl, ethyl, propyl, butyl, pentyl, and hexyl; and aryl such asphenyl, tolyl, xylyl and benzyl. Subscript f has a value ranging from 0to 10, alternatively 0.

The endcapper may provide the benefit of producing a looser network ofhigher tensile properties when used as a mole percentage of theavailable SiH in the system. The amount of endcapper added may rangefrom 0 to 15%, alternatively 2% to 15%, and alternatively 10%, based onthe combined weight of all components used in the process.

A secondary benefit of having an endcapper in the process is initialreduction in viscosity prior to reaction, which may facilitate thereaction and reduce the tendency for gelation due to insufficient mixingand local gel formation.

The weight percent of silicon bonded hydrogen atoms in thecomponents/weight percent of unsaturated organic groups capable ofundergoing hydrosilylation in the components (commonly referred to asSiH_(tot)/Vi_(tot) ratio) may range from 1/1.4 to 1/1, alternatively1/1.2 to 1/1.1. In this ratio, SiH_(tot) refers to the amount of siliconbonded hydrogen atoms in any of the components of the silicone reactivediluent. Vi_(tot) refers to the total amount of aliphaticallyunsaturated organic groups in the silicone reactive diluent.

In certain embodiments, the silicone reactive diluent (III) of the firstembodiment is formed by:

1) concurrently reacting components comprising:

-   -   a) a polyorganohydrogensiloxane having an average of 10 to 200        silicon atoms per molecule; and    -   b) a reactive species having, per molecule, at least 1        aliphatically unsaturated organic group and 1 or more curable        groups;    -   in the presence of c) an isomer reducing agent and (d) a        hydrosilylation catalyst, and optionally f) a polymerization        inhibitor and g) an endcapper.

The resulting mixture of a), b), c), d) and optionally f) and g) may besheared before addition of component c) at room temperature. Thereaction may then be initiated by raising the temperature to a rangefrom 50° C. to 100° C., alternatively 70° C. to 85° C., and maintainingthe temperature until all of the SiH has reacted, as measured by thetime needed for the SiH peak as observed by Fourier Transform Infra Redspectroscopy (FT-IR) at about 2170 cm⁻¹, to be reduced into thebackground of the spectra.

Next, the catalyst inhibitor e) is added to the resulting mixture todeactivate the hydrosilylation catalyst c). In certain embodiments, theintroduction of the catalyst inhibitor e) is done after reducing thetemperature of the reaction mixture of a), b), c), d) and optionally f)and g) below the minimum reaction temperature of 50° C., such as at roomtemperature. The formed silicone reactive diluent (III) may be storedfor subsequent use.

In an alternative or second embodiment, the silicone reactive diluent(III) may be formed as the reaction product of a reaction of:

a) a siloxane compound according to the formula:

wherein:

-   -   R is a monovalent hydrocarbon having 1 to 6 carbon atoms,    -   R′ is a monovalent hydrocarbon having 3 to 12 carbon atoms.    -   R″ is H or CH₃, and    -   the subscript m and n each independently have a value from 1 to        10, and    -   b) a polyorganosiloxane having an average, per molecule, of at        least 2 aliphatically unsaturated organic groups,

in the presence of c) a first hydrosilylation catalyst and d) aninhibitor for the first hydrosilylation catalyst, as well as otheradditional optional components.

Component b) of the silicone reactive diluent (III) of the secondembodiment is a polyorganosiloxane having an average, per molecule, ofat least 2 aliphatically unsaturated organic groups, which are capableof undergoing a hydrosilylation reaction with a silicon bonded hydrogenatom of the siloxane compound a). Component b) may have a linear orbranched structure. Alternatively, component b) may have a linearstructure. Component b) may be a combination comprising two or morepolyorganosiloxanes that differ in at least one of the followingproperties: structure, viscosity, degree of polymerization, andsequence.

Component b) has a minimum average degree of polymerization (average DP)of 10. Alternatively, average DP of component b) may range from 10 to1000 alternatively 100 to 200. The distribution DP ofpolyorganosiloxanes of component a) can be bimodal. For example,component b) may comprise one alkenyl terminated polydiorganosiloxanewith a DP of 2 and another alkenyl terminated polydiorganosiloxane witha DP higher than 10, provided that average DP of thepolydiorganosiloxanes ranges from 10 to 1000. However, suitablepolyorganosiloxanes for use in component b) have a minimum degree ofpolymerization (DP) of 10, provided that polyorganosiloxanes with DPless than 10 are combined with polyorganosiloxanes having DP greaterthan 10. Suitable polydiorganosiloxanes for component a) are known inthe art and are commercially available. For example, Dow Corning®SFD-128 has DP ranging from 800 to 1000, Dow Corning® SFD-120 has DPranging from 600 to 700, Dow Corning® 7038 has DP of 100, and DowCorning® SFD-119 has DP of 150. All of these are vinyl-terminatedpolydimethylsiloxanes are commercially available from Dow CorningCorporation of Midland, Mich., USA. When component b) has a bimodaldistribution, the polyorganosiloxane with the lower DP (low DPpolyorganosiloxane) is present in a lower amount than thepolyorganosiloxane with the higher DP (high DP polyorganosiloxane). Forexample, in a bimodal distribution, the ratio of low DPpolyorganosiloxane/high DP polyorganosiloxane may range from 10/90 to25/75.

Component b) is exemplified by polyorganosiloxanes of formula (I),formula (II), or a combination thereof. Formula (I) is R¹ ₂R²SiO(R¹₂SiO)_(a)(R¹R²SiO)_(b)SiR¹ ₂R², and formula (II) is R¹ ₃SiO(R¹₂SiO)_(d)(R¹R²SiO)_(d)SiR¹ ₃. In these formulae, each R¹ isindependently a monovalent organic group free of aliphatic unsaturation,each R² is independently an aliphatically unsaturated organic group,subscript a has an average value ranging from 2 to 1000, subscript b hasan average value ranging from 0 to 1000, subscript c has an averagevalue ranging from 0 to 1000, and subscript d has an average valueranging from 4 to 1000. In formulae (I) and (II), 10≦(a+b)≦1000 and10≦(c+d)≦1000.

Suitable monovalent organic groups for R¹ include, but are not limitedto, monovalent hydrocarbon groups exemplified by alkyl such as methyl,ethyl, propyl, butyl, pentyl, octyl, undecyl, and octadecyl; cycloalkylsuch as cyclohexyl; and aryl such as phenyl, tolyl, xylyl, benzyl, and2-phenylethyl. Each R² is independently an aliphatically unsaturatedmonovalent organic group. R² may be an aliphatically unsaturatedmonovalent hydrocarbon group exemplified by alkenyl groups such asvinyl, allyl, propenyl, and butenyl; and alkynyl groups such as ethynyland propynyl.

Component b) may comprise a polydiorganosiloxane such as i)dimethylvinylsiloxy-terminated polydimethylsiloxane, ii)dimethylvinylsiloxy-terminatedpoly(dimethylsiloxane/methylvinylsiloxane), iii)dimethylvinylsiloxy-terminated polymethylvinylsiloxane, iv)trimethylsiloxy-terminated poly(dimethylsiloxane/methylvinylsiloxane),v) trimethylsiloxy-terminated polymethylvinylsiloxane, vi)dimethylvinylsiloxy-terminatedpoly(dimethylsiloxane/methylphenylsiloxane), vii)dimethylvinylsiloxy-terminated poly(dimethylsiloxane/diphenylsiloxane),viii) phenyl,methyl,vinyl-siloxy-terminated polydimethylsiloxane, ix)dimethylhexenylsiloxy-terminated polydimethylsiloxane, x)dimethylhexenylsiloxy-terminatedpoly(dimethylsiloxane/methylhexenylsiloxane), xi)dimethylhexenylsiloxy-terminated polymethylhexenylsiloxane, xii)trimethylsiloxy-terminated poly(dimethylsiloxane/methylhexenylsiloxane),or xiii) a combination thereof.

The relative amounts of the siloxane compound a) and thepolyorganosiloxane b) in the silicone reactive diluent (III) of thesecond embodiment may vary such that the SiH:vinyl weight ratio rangesfrom 0.8:1 to 1:1.

Suitable hydrosilylation catalysts d) and inhibitors for thehydrosilylation catalyst e) that may be used in forming of the siliconereactive diluent (III) of the second embodiment include each of thehydrosilylation catalysts described above and not repeated herein.

In addition to Components a)-d), other optional components may beutilized in forming the silicone reactive diluent (III) according tothis alternative embodiment, including f) a polymerization inhibitor andg) an endcapper, the descriptions of which are the same as provided asoptional components f) and g) for forming the silicone reactive diluent(III) according to the first embodiment and not repeated herein.

Component (IV) of the thermally conductive thermal radical cure siliconecomposition is a clustered functional polyorganosiloxane. Examples ofclustered functional polyorganosiloxane that may be included herein aredisclosed in U.S. Patent Publication No. 2012/0245272 to Dent et. al.Another alternative clustered functional polyorganosiloxane that may beused herein comprises the reaction product of a reaction of components(a)-(e) of the thermally conductive clustered functionalpolyorganopolysiloxane (I) described above and including additionaloptional components as described in Dent et. al.

Component (V) of the thermally conductive thermal radical cure siliconecomposition is a moisture cure initiator (i.e, a condensation reactioncatalyst). Examples of condensation reaction catalysts are known in theart and are disclosed in U.S. Pat. Nos. 4,962,076; 5,051,455; 5,053,442;4,753,977 at col. 4, line 35 to col. 5, line 57; and 4,143,088 at col.7, line 15 to col. 10, line 35. The amount of the condensation reactioncatalyst depends on various factors including the type of catalystselected and the choice of the remaining components in the composition,however the amount of the condensation reaction catalyst may range from0.001% to 5% based on the weight of thermally conductive thermallyradical cure adhesive composition.

Suitable condensation reaction catalyst may be a Lewis acid; a primary,secondary, or tertiary organic amine; a metal oxide; a titaniumcompound; a tin compound; a zirconium compound; or a combinationthereof. The condensation reaction catalyst may comprise a carboxylicacid salt of a metal ranging from lead to manganese inclusive in theelectromotive series of metals. Alternatively, the condensation reactioncatalyst may comprise a chelated titanium compound, a titanate such as atetraalkoxytitanate, a titanium ester, or a combination thereof.Examples of suitable titanium compounds include, but are not limited to,diisopropoxytitanium bis(ethylacetoacetate), tetrabutoxy titanate,tetrabutyltitanate, tetraisopropyltitanate, andbis-(ethoxyacetoacetonate)diisopropoxy titanium (IV), and a combinationthereof. Alternatively the condensation reaction catalyst may comprise atin compound such as dibutyltin diacetate; dibutyltin dilaurate; dibutyltin oxide; stannous octoate; tin oxide; a titanium ester, such astetrabutyl titanate, tetraethylhexyl titanate and tetraphenyltitanate; asiloxytitanate, such as tetrakis(trimethylsiloxy)titanium andbis(trimethylsiloxy)-bis(isopropoxy)titanium; and abetadicarbonyltitanium compound, such as bis(acetylacetonyl)diisopropyltitanate; or a combination thereof. Alternatively, the condensationreaction catalyst may comprise an amine, such as hexylamine; or anacetate or quat salt of an amine.

Component (VI) of the thermally conductive thermal radical cure siliconecomposition is a crosslinker. The type and amount of crosslinker willdepend on various factors including the type and amount of curablegroups on component (VII).

In certain embodiments, the crosslinker (VI) is a condensation reactioncrosslinker that may be selected from, for example, trialkoxysilanesexemplified by propyltrimethoxysilane, phenyltrimethoxysilane,glycidoxypropyltrimethoxysilane, ethyltrimethoxysilane,aminopropyltrimethoxysilane, aminoethylaminopropyltrimethoxysilane,methyltrimethoxysilane, phenyl trimethoxysilane, andmethyltriethoxysilane; acetoxysilanes such as methyltriacetoxysilane orethyltriacetoxysilane; ketoximosilanes such asmethyltri(methylethylketoximo)silane, tetra(methylethylketoximo)silane,methyltris(methylethylketoximo)silane, andvinyltris(methylethylketoximo) silane; alkyl orthosilicates such astetraethyl orthosilicate, tetramethoxysilane, tetraethoxysilane, andcondensation products of these orthosilicates, which are typicallyreferred to as alkyl polysilicates; methylvinyl bis(n-methylacetamido)silane; and a combination thereof.

In certain embodiments, the amount of crosslinker (VI) utilized in thethermally conductive thermal radical cure silicone composition isdependent upon numerous factors, but is based primarily upon the typeand amount of curable groups contained in components (I) and (II). Incertain embodiments, the amount of crosslinker (VI) is from 0.1 to 50weight percent, such as from 0.5 to 30 weight percent, based upon thetotal weight of component (VII) below.

Component (VII) of the thermally conductive thermal radical curesilicone composition is a moisture cure polymer that comprises anorganopolysiloxane polymer of the formula: Component (VII) is a moisturecure polymer that comprises an organopolysiloxane polymer of theformula: (OR⁷)_(3-z)R⁶ _(z)Si-Q-(R²⁵ ₂SiO_(2/2))_(y)-Q-SiR⁶_(z)(OR⁷)_(3-z), wherein each R²⁵ is independently a monovalenthydrocarbon radical having 1 to 6 carbon atoms, each R⁶ independently isa monovalent hydrocarbon radical having 1 to 6 carbon atoms, each R⁷independently is selected from the group consisting of an alkyl radicaland alkoxyalkyl radical, Q is a divalent linking radical, the subscriptz has a value of 0, 1 or 2, and the subscript y has a value of 60 to1000.

In certain embodiments, the moisture cure polymer (VI) is present in anamount ranging from 0.1 to 5 weight percent based on the weight ofthermally conductive thermally radical cure adhesive composition.

The Q radical is a divalent linking radical linking the silicon atom ofthe curing radical to a silicon atom of the resin. Q is typicallyselected from the types of divalent radicals that are used to linksilicon atoms in a hydrolytically stable manner and include, but are notlimited to, hydrocarbons such as alkylene, for example ethylene,propylene, and isobutylene and phenylene; siloxanes such as, forexample, polydimethylsiloxane; and combinations thereof. Preferably, thenumber of hydrocarbon radical units in the Q divalent linking radicalnumbers from 2 to 12, alternatively 2, and the number of siloxaneradical units in the Q divalent linking radical numbers from 0 to 20,alternatively 2.

Component (VIII) of the thermally conductive thermal radical curesilicone composition is a solvent. Suitable solvents are exemplified byorganic solvents such as toluene, xylene, acetone, methylethylketone,methyl isobutyl ketone, hexane, heptane, alcohols such as decyl alcoholor undecyl alcohol, and a combination thereof; and non-crosslinkablesilicone solvents such as trimethylsiloxy-terminatedpolydimethylsiloxanes, trimethylsiloxy-terminatedpolymethylphenylsiloxanes, and a combination thereof. Examples ofsilicone solvents are known in the art and are commercially available,for example, as Dow Corning® OS Fluids from Dow Corning Corporation ofMidland, Mich., U.S.A. The amount of component (VIII) may range from0.001% to 90% based on the weight of thermally conductive thermallyradical cure adhesive composition.

Component (IX) of the thermally conductive thermal radical cure siliconecomposition is an adhesion promoter. Examples of suitable adhesionpromoters include an alkoxysilane such as an epoxy-functionalalkoxysilane, or a mercapto-functional compound; a combination of analkoxysilane and a hydroxy-functional polyorganosiloxane; amercapto-functional compound; an unsaturated compound; anepoxy-functional silane; an epoxy-functional siloxane; a combination,such as a reaction product, of an epoxy-functional silane orepoxy-functional siloxane and a hydroxy-functional polyorganosiloxane;or a combination thereof. Suitable adhesion promoters are known in theart and are commercially available. For example, Silquest® A186 isbeta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane which is commerciallyavailable from Crompton OSi Specialties of Middlebury, Conn., USA.CD9050 is a monofunctional acid ester useful as an adhesion promoterthat provides adhesion to metal substrates and is designed for radiationcurable compositions. CD9050 is commercially available from Sartomer Co.SR489D is tridecyl acrylate, SR395 is isodecyl acrylate, SR257 isstearyl acrylate, SR506 is isobornyl acrylate, SR833S is tricyclodecanedimethanol diacrylate, SR238 is 1,6 hexanediol diacrylate, and SR351 istrimethylol propane triacrylate, all of which are also commerciallyavailable from Sartomer Co. The amount of adhesion promoter (IX) addedto the composition depends on various factors including the specificadhesion promoter selected, the other components of the composition, andthe end use of the composition, however, the amount may range from 0.01%to 5% based on the weight of thermally conductive thermally radical cureadhesive composition. Other suitable adhesion promoters, which areuseful to promote adhesion to metals, include maleic anhydride,methacrylic anhydride, and glycidyl methacrylate.

Component (IX) can be an unsaturated or epoxy-functional compound.Suitable epoxy-functional compounds are known in the art andcommercially available, see for example, U.S. Pat. Nos. 4,087,585;5,194,649; 5,248,715; and 5,744,507 (at col. 4-5). Component (g) maycomprise an unsaturated or epoxy-functional alkoxysilane. For example,the functional alkoxysilane can have the formula R²⁰_(v)Si(OR²¹)_((4-v)), where subscript v is 1, 2, or 3, alternatively vis 1.

Each R²⁰ is independently a monovalent organic group with the provisothat at least one R²⁰ is an unsaturated organic group or anepoxy-functional organic group. Epoxy-functional organic groups for R²⁰are exemplified by 3-glycidoxypropyl and (epoxycyclohexyl)ethyl.Unsaturated organic groups for R²⁰ are exemplified by3-methacryloyloxypropyl, 3-acryloyloxypropyl, and unsaturated monovalenthydrocarbon groups such as vinyl, allyl, hexenyl, undecylenyl.

Each R²¹ is independently an unsubstituted, saturated hydrocarbon groupof 1 to 4 carbon atoms, alternatively 1 to 2 carbon atoms. R²¹ isexemplified by methyl, ethyl, propyl, and butyl.

Examples of suitable epoxy-functional alkoxysilanes include3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane,(epoxycyclohexyl)ethyldimethoxysilane,(epoxycyclohexyl)ethyldiethoxysilane and combinations thereof. Examplesof suitable unsaturated alkoxysilanes include vinyltrimethoxysilane,allyltrimethoxysilane, allyltriethoxysilane, hexenyltrimethoxysilane,undecylenyltrimethoxysilane, 3-methacryloyloxypropyl trimethoxysilane,3-methacryloyloxypropyl triethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyl triethoxysilane, and combinationsthereof. Alternatively, examples of suitable adhesion promoters includeglycidoxypropyltrimethoxysilane and a combination ofglycidoxypropyltrimethoxysilane with an aluminum chelate or zirconiumchelate.

Component (IX) may comprise an epoxy-functional siloxane such as areaction product of a hydroxy-terminated polyorganosiloxane with anepoxy-functional alkoxysilane, as described above, or a physical blendof the hydroxy-terminated polyorganosiloxane with the epoxy-functionalalkoxysilane. Component (IX) may comprise a combination of anepoxy-functional alkoxysilane and an epoxy-functional siloxane. Forexample, component (VII) is exemplified by a mixture of3-glycidoxypropyltrimethoxysilane and a reaction product ofhydroxy-terminated methylvinylsiloxane with3-glycidoxypropyltrimethoxysilane, or a mixture of3-glycidoxypropyltrimethoxysilane and a hydroxy-terminatedmethylvinylsiloxane, or a mixture of 3-glycidoxypropyltrimethoxysilaneand a hydroxy-terminated methylvinyl/dimethylsiloxane copolymer. Whenused as a physical blend rather than as a reaction product, thesecomponents may be stored separately in multiple-part kits.

Suitable mercapto-functional compounds include an organomercaptan, amercapto containing silane, or a combination thereof. Suitable mercaptocontaining silanes include 3-mercaptopropyltrimethoxysilane. Suitablemercapto-functional compounds are disclosed in U.S. Pat. No. 4,962,076.One skilled in the art would recognize that certain components describedherein may be added to the composition for more than one or differentpurposes. For example, alkoxysilanes may be use as adhesion promoters,filler treating agents, and/or as crosslinking agents in condensationreaction curable silicone compositions.

Component (X) of the thermally conductive thermal radical cure siliconecomposition is a colorant (e.g., dye or pigment). Examples of suitablecolorants include carbon black, Stan-Tone 40SP03 Blue (which iscommercially available from PolyOne) and Colorant BA 33 Iron Oxidepigment (which is commercially available from Cathay Pigments (USA),Inc. Valparaiso, Ind. 46383 USA). Examples of colorants are known in theart and are disclosed in U.S. Pat. Nos. 4,962,076; 5,051,455; and5,053,442. The amount of colorant added to the curable siliconecomposition depends on various factors including the other components ofthe composition, and the type of colorant selected, however, the amountmay range from 0.001% to 20% based on the weight of the composition.

Component (XI) of the thermally conductive thermal radical cure siliconecomposition is a reactive diluent that is different than the siliconereactive diluent (III). Component (XI) may be diluent that reacts with afunctional group on the thermally conductive clustered functionalpolyorganosiloxane (I). The reactive diluent may be a monofunctionalreactive diluent, a difunctional reactive diluent, a polyfunctionalreactive diluent, or a combination thereof. The reactive diluent (XI)selected will depend on various factors including the curable groups onon the thermally conductive clustered functional polyorganosiloxane (I).However, examples of suitable reactive diluents include an acrylate, ananhydride such as a maleic anhydride or methacrylic anhydride, an epoxysuch as a monofunctional epoxy compound, a methacrylate such as glycidylmethacrylate, an oxetane, a vinyl acetate, a vinyl ester, a vinyl ether,a fluoro alkyl vinyl ether, a vinyl pyrrolidone such as N-vinylpyrrolidone, a styrene, or a combination thereof.

Mono-functional acrylate and methacrylate esters are commerciallyavailable from companies such as Sartomer, Rohm Haas, Hitachi Chemical,Arkema, Inc., Cytec, Sans Ester Corp, Rahn, and Bomar Specialties Co.Specific examples include methyl acrylate; methyl methacrylate; ethylacrylate; ethyl methacrylate; butyl acrylate; butyl methacrylate;cyclohexyl acrylate; hexyl acrylate; 2-ethylhexyl acrylate; isodecylmethacrylate; isobornyl methacrylate; hydroxyethyl methacrylate;hydroxypropyl acrylate; hydroxypropyl methacrylate; n-octyl acrylate;cyclohexyl methacrylate; hexyl methacrylate; 2-ethylhexyl methacrylate;decyl methacrylate; dodecyl methacrylate; lauryl acrylate; tert-butylmethacrylate; acrylamide; N-methyl acrylamide; diacetone acrylamide;N-tert-butyl acrylam ide; N-tert-octyl acrylam ide; N-butoxyacrylam ide;gam ma-methacryloxypropyl trimethoxysilane; dicyclopentadienyloxyethylmethacrylate; 2-cyanoethyl acrylate; 3-cyanopropyl acrylate;tetrahydrofurfuryl methacrylate; tetrahydrofurfuryl acrylate; glycidylacrylate; acrylic acid; methacrylic acid; itaconic acid; glycidylmethacrylate; 1,12 dodecanediol dimethacrylate; 1,3-butylene glycoldiacrylate; 1,3-butylene glycol dimethacrylate; 1,3-butylene glycoldimethacrylate; 1,4-butanediol diacrylate; 1,4-butanedioldimethacrylate; 1,4-butanediol dimethacrylate; 1,6 hexanedioldiacrylate; 1,6 hexanediol dimethacrylate; alkoxylated cyclohexanedimethanol diacrylate; alkoxylated hexanediol diacrylate; alkoxylatedneopentyl glycol diacrylate; cyclohexane dimethanol diacrylate;cyclohexane dimethanol dimethacrylate; diethylene glycol diacrylate;diethylene glycol dimethacrylate; dipropylene glycol diacrylate;ethoxylated bisphenol a diacrylate; ethoxylated bisphenol adimethacrylate; ethylene glycol dimethacrylate; neopentyl glycoldiacrylate; neopentyl glycol dimethacrylate; polypropyleneglycoldimethacrylate; propoxylated neopentyl glycol diacrylate;propoxylated neopentyl glycol diacrylate; tricyclodecane dimethanoldiacrylate; triethylene glycol diacrylate; trimethylolpropanetriacrylate; trimethylolpropane trimethacrylate; tris (2-hydroxy ethyl)isocyanurate triacrylate; tris (2-hydroxy ethyl) isocyanuratetriacrylate; n,n′-m-phenylenedimaleimide; triallyl cyanurate; triallylisocyanurate; metallic diacrylate; metallic dimethacrylate; metallicmonomethacrylate; metallic diacrylate (difunctional); metallicdimethacrylate (difunctional); triethoxysilylpropyl methacrylate;tributoxysilylpropyl methacrylate; dimethoxymethylsilylpropylmethacrylate; diethoxymethylsilylpropyl methacrylate;dibutoxymethylsilylpropyl methacrylate; diisopropoxymethylsilylpropylmethacrylate; dimethoxysilylpropyl methacrylate; diethoxysilylpropylmethacrylate; dibutoxysilylpropyl methacrylate; diisopropoxysilylpropylmethacrylate; trimethoxysilylpropyl acrylate; triethoxysilylpropylacrylate; tributoxysilylpropyl acrylate; dimethoxymethylsilylpropylacrylate; diethoxymethylsilylpropyl acrylate; dibutoxymethylsilylpropylacrylate; diisopropoxymethylsilylpropyl acrylate; dimethoxysilylpropylacrylate; diethoxysilylpropyl acrylate; dibutoxysilylpropyl acrylate;and diisopropoxysilylpropyl acrylate.

Examples of suitable vinyl ethers include, but are not limited tobutanediol divinyl ether, cyclohexanedimethanol divinyl ether,cyclohexanedimethanol monovinyl ether, cyclohexyl vinyl ether,diethyleneglycol divinyl ether, diethyleneglycol monovinyl ether,dodecyl vinyl ether, ethyl vinyl ether, hydroxybutyl vinyl ether,isobutyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether,n-propyl vinyl ether, octadecyl vinyl ether, triethyleneglycol divinylether, and combinations thereof. Vinyl ethers are known in the art andcommercially available from BASF AG of Germany, Europe. The amount ofcomponent (IX) depends on various factors such as the specific reactivediluent selected, but the amount may range from 0.01 to 10% based on theweight of thermally conductive thermally radical cure adhesivecomposition. One skilled in the art would recognize that some of thereactive diluents described herein (such as the difunctional andpolyfunctional acrylates and methacrylates) may also be used in additionto, or instead of, the reactive species described above as component c)of (I).

Component (XII) of the thermally conductive thermal radical curesilicone composition is a corrosion inhibitor. Examples of suitablecorrosion inhibitors include benzotriazole, mercaptabenzotriazole,mercaptobenzothiazole, and commercially available corrosion inhibitorssuch as 2,5-dimercapto-1,3,4-thiadiazole derivative (CUVAN® 826) andalkylthiadiazole (CUVAN® 484) from R. T. Vanderbilt. The amount ofcomponent (XII) may range from 0.05% to 0.5% based on the weight ofthermally conductive thermally radical cure adhesive composition.

Component (XIII) of the thermally conductive thermal radical curesilicone composition is a polymerization inhibitor. Examples of suitablepolymerization inhibitors for acrylate and methacrylate curable groupsinclude, but are not limited to:2,6,-Di-tert-butyl-4-(dimethylaminomethyl)phenol (DBAP), hydroquinone(HQ); 4-methoxyphenol (MEHQ); 4-ethoxyphenol; 4-propoxyphenol;4-butoxyphenol; 4-heptoxyphenol; butylated hydroxytoluene (BHT);hydroquinone monobenzylether; 1,2-dihydroxybenzene; 2-methoxyphenol;2,5-dichlorohydroquinone; 2,5-di-tert-butylhydroquinone;2-acetylhydroquinone; hydroquinone monobenzoate; 1,4-dimercaptobenzene;1,2-dimercaptobenzene; 2,3,5-trimethylhydroquinone; 4-aminophenol;2-aminophenol; 2-N, N-dimethylaminophenol; 2-mercaptophenol;4-mercaptophenol; catechol monobutylether; 4-ethylaminophenol;2,3-dihydroxyacetophenone; pyrogallol-1,2-dimethylether;2-methylthiophenol; t-butyl catechol; di-tert-butylnitroxide;di-tert-amylnitroxide; 2,2,6,6-tetramethyl-piperidinyloxy;4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy;4-oxo-2,2,6,6-tetramethyl-piperidinyloxy;4-dimethylamino-2,2,6,6-tetramethyl-piperidinyloxy;4-amino-2,2,6,6-tetramethyl-piperidinyloxy;4-ethanoloxy-2,2,6,6-tetramethyl-piperidinyloxy;2,2,5,5-tetramethyl-pyrrolidinyloxy;3-amino-2,2,5,5-tetramethyl-pyrrolidinyloxy;2,2,5,5-tetramethyl-1-oxa-3-azacyclopentyl-3-oxy;2,2,5,5-tetramethyl-3-pyrrolinyl-1-oxy-3-carboxylic acid;2,2,3,3,5,5,6,6-octamethyl-1,4-diazacyclohexyl-1,4-dioxy; salts of4-nitrosophenolate; 2-nitrosophenol; 4-nitrosophenol; copperdimethyldithiocarbamate; copper diethyldithiocarbamate; copperdibutyldithiocarbamate; copper salicylate; methylene blue; iron;phenothiazine (PTZ); 3-oxophenothiazine; 5-oxophenothiazine;phenothiazine dimer; 1,4-benzenediamine;N-(1,4-dimethylpentyl)-N′-phenyl-1,4-benzenediamine;N-(1,3-dimethylbutyl)-N′-phenyl-1,4-benzenediamine;N-nitrosophenylhydroxylamine and salts thereof; nitric oxide;nitrobenzene; p-benzoquinone; pentaerythrityltetrakis(3-laurylthiopropionate); dilauryl thiodipropionate; distearyllthiodipropionate; ditridecyl thiodipropionate; tetrakis[methylene3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane; thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate];octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;isotridecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;N,N′-hexamethyl (3,5-di-tertbutyl-4-hydroxyhydrocinnamamide);iso-octyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate;2,2′-ethylidenebis-(4,6-di-tert-butylphenol);1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl) benzene;4,6-bis(octylthiomethyl)-o-cresol; triethyleneglycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate;tris-(3,5-di-tert-butylhydroxybenzyl) isocyanurate;tris(2,4-di-tert-butylphenyl) phosphate; distearyl pentaerythritoldiphosphite; bis(2,4-di-tert-butyl phenyl)pentaerythritol diphosphite;2,5-di-tert-amyl-hydroquinone; or isomers thereof; combinations of twoor more thereof; or combinations of one or more of the above withmolecular oxygen. When present, the polymerization inhibitor may beadded to the curable silicone composition in an amount ranging from 100ppm to 4,000 ppm. Polymerization inhibitors are known in the art and aredisclosed, for example in EP 1 359 137.

Component (XIV) of the thermally conductive thermal radical curesilicone composition is an acid acceptor. The acid acceptor may comprisea metal oxide such as magnesium oxide. Acid acceptors are known in theart and are commercially available under tradenames including RhenofitF, Star Mag CX-50, Star Mag CX-150, BLP-3, and MaxOx98LR. Rhenofit F wascalcium oxide from Rhein Chemie Corporation of Chardon, Ohio, USA. StarMag CX-50 was magnesium oxide from Merrand International Corp. ofPortsmouth, N.H., USA. MagOX 98LR was magnesium oxide from PremierChemicals LLC of W. Conshohocken, Pa., USA. BLP-3 was calcium carbonatewas Omya Americas of Cincinnati, Ohio, USA.

The thermally conductive thermal radical cure silicone compositions ofthe present invention, as noted above, are preferably formed in a methodknown the “In Situ Method”.

In the In Situ Method, in one embodiment, the silicone reactive diluent(III) is premade (in accordance with any possible embodiment describedabove) and introduced as an optional component during the methoddescribed below, while the thermally conductive clustered functionalpolyorganosiloxane (I) is made during the process.

In Step 1 of the process, a masterbatch is formed in a vessel thatincludes the filler (f) and a polyorganosiloxane having an average, permolecule, of at least 2 aliphatically unsaturated organic groups (i.e.,component (a) of the thermally conductive clustered functionalpolyorganosiloxane (I), described above). The mixture may be sheared atroom temperature to homogeneity.

The filler (f) for Step 1) includes a thermally conductive filler andcan be one size or can be the combination of differing particle size anddifferent particle size distribution.

In certain embodiments, the majority of the filler (f) added in thisfirst step are larger surface area particles (i.e., those having anaverage surface area of 0.5 m²/gram or greater).

Next, in Step 2, a filler treating agent (g) is added to the mixture andsheared at room temperature to homogeneity. Alternatively, the fillertreating agent (g) may be added concurrently to the filler (f) andpolyorganosiloxane (a) in Step 1.

Next, in Step 3, the mixture is heated to a temperature sufficient toinsure the in situ treating of the thermally conductive fillers with thefiller treating agent (g) in the presence of the polyorganosiloxane (a).The treating reaction may be initiated by raising the temperature to arange of 50° C. to 300° C., alternatively to a range of 100° C. to 150°C.

Next, in Step 4, the reaction product of Step 3 is cooled to below 30°C., such as to 10 to 15° C., wherein it is mixed with the rest of thecomponents that comprise the thermally conductive clustered functionalpolyorganosiloxane (I), namely, the polyorganohydrogensiloxane having anaverage of 4 to 15 silicon atoms per molecule (component (b)), thereactive species having, per molecule, at least 1 aliphaticallyunsaturated organic group and 1 or more curable groups (component (c)the hydrosilylation catalyst (component (d), and the isomer reducingagent (component (e). In certain embodiments, a polymerization inhibitor(XIII) may be added as a part of Step 4.

Next, in Optional Step 5, the processes described above may furthercomprise the steps of adding a catalyst inhibitor, such as the catalystinhibitor e) described above with respect to the method for formingsilicone reactive diluent (III) in the first embodiment, to deactivatethe hydrosilylation catalyst after Step 4, and purifying the product ofstep 4.

Next, in Step 6, the resulting mixture of Step 4 or Step 5 may besheared at room temperature.

In Step 7, the clustered functional reaction may then be initiated byraising the temperature of the mixture to 50° C. to 100° C.,alternatively 70° C. to 85° C., and maintaining the temperature untilsubstantially all of the SiH of the mixture of Step 4 has reacted, asmeasured by the time needed for the SiH peak as observed by FourierTransform Infra Red spectroscopy (FT-IR) at about 2170 cm⁻¹ to bereduced into the background of the spectra.

After completion of Step 7, in Step 8, the mixture is cooled to below50° C., wherein optionally the silicone reactive diluent (III) is addedto the mixture. In addition, other optional components, includingadditional filler (f), additional filler treating agent (g), or acombination thereof may also be introduced in Step 8 and the resultantmixture is mixed to homogeneity.

The filler (f) introduced in Step 8 includes a thermally conductivefiller and can be one size or can be the combination of differingparticle size and different particle size distribution, including largersurface area particles particles (i.e., those having an average surfacearea of 0.5 m²/gram or greater) and smaller surface area particles(i.e., those having an average surface area of less than 0.5 m²/gram).

In addition, the filler (f) introduced during Step 8 can havealkylthiols such as octadecyl mercaptan and others, and fatty acids suchas oleic acid, stearic acid, titanates, titanate coupling agents,zirconate coupling agents, and a combination thereof. Stated anotherway, the filler (f) introduced Step 8 is hereinafter referred to a“dirty filler.” Conversely, the filler (f) added in Step 1 is not a“dirty filler”, but is a purer form of the filler that does not includealkylthiols such as octadecyl mercaptan and others, and fatty acids suchas oleic acid, stearic acid, titanates, titanate coupling agents,zirconate coupling agents, and a combination thereof. Stated anotherway, the filler of Step 1 is a highly pure filler.

Next, in Step 9, the mixture can be maintained at room temperature orheated to an elevated temperature 50° C. to 110° C., alternatively 70°C. to 85° C., in order to treat any additional filler added in Step 8.

In certain embodiments, Steps 8 and 9 can be repeated until a desiredthermally conductive filler loading level for the silicone compositionis achieved.

Next, in Step 10, the temperature of the reaction vessel is cooled andany one or more of the additional components (III)-(XIV) are blendedwith the resultant mixture and mixed to homogeneity. In certainembodiments, the temperature is cooled to below 50° C. prior to theaddition of the additional components (III)-(XIV). Each of theadditional components (III)-(XIV) may be added to the vesselsequentially, or all at once, or in sequential groups.

Finally, in Step 11, the temperature is cooled to below 30° C. and theradical initiator (II) is added to the mixture and mixed to homogeneityto form the thermally conductive thermal radical cure adhesivecomposition. Alternatively, in certain embodiments, the radicalinitiator (II) may be added as a part of Step 10 when the temperature isbelow 30° C.

The resultant thermally conductive thermal radical cure siliconecomposition formed in accordance with the In Situ Method achieved athermal conductivity greater than 0.5 W/mK (watts per meter Kelvin),alternatively greater than 1 W/mK, alternatively greater than 1.5 W/mK.

The thermally conductive thermal radical cure silicone compositionformed by the In Situ Method as described above, and cured siliconecoatings prepared by curing the resultant thermally conductive thermalradical cure adhesive composition, are useful in electronicsapplications, including both microelectronics and macroelectronicsapplications as well as optoelectronics applications and thermallyconductive electronics applications, such as making thermally conductiveadhesives. As the thermally conductive thermal radical cure siliconecompositions of the present invention are cured both thermal radicalcure and moisture cure, they may be utilized on a wider variety ofsubstrates than traditional radical cure adhesive compositions ormoisture cure adhesive compositions.

Cured silicone adhesives prepared from such a thermally conductivethermal radical cure silicone composition may adhere to variouselectronics substrates, including metals such as aluminum, copper, andelectroless nickel; as well as polymeric substrates such as FR4, Nylon,polycarbonate, Lucite (which is polymethylmethacrylate, PMMA),polybutylene terephthalate (PBT), and Solvay liquid crystal polymers.

Composite articles according to the invention preferably consist of theafore-mentioned thermally conductive thermal radical cure siliconecompositions, and can be disposed or applied to a single substrate orbetween multiple substrates. At least one surface of the substrate towhich the thermally conductive thermal radical cure siliconecompositions is applied should have a polymeric or largely inorganicsurface. Any additional substrates can be organic, thermoplastic,thermosetting, metal, ceramic, or another suitable inorganic material.The substrate(s) can be multi-layered such as a printed circuit board inwhich case there is obtained improved adhesion between the thermallyconductive thermal radical cure silicone compositions and the substrateor substrates of the composite article.

Composite articles are made by bonding the thermally conductive thermalradical cure silicone compositions to at least one surface of thesubstrate in the composite article. This is carried out by curing thecomposition at temperatures below 150° C. alternatively at 70-100° C.,and achieving sufficient adherence such that the conductive curablecomposition and the substrate are bonded together securely to form thecomposite article.

When the polymeric substrate is a material such as glass reinforcedpolybutylene terephthalate (PBT), the upper temperature for curing thecurable composition on the surface of the substrate may be less than 80°C. For maximum benefit, the temperature should range from −40° C. to 80°C., alternatively from 0° C. to 60° C., alternatively from 25° C. to 60°C. The time for curing the composition on the substrate can range from 5seconds to 24 hours, alternatively from 30 seconds to 2 hours. This willassure that the composition is fully cured and fully adhered to thesubstrate. The curable composition can be applied to a substrate bymeter mixing, extruding, and/or using robotic or manual application.

Fully bonded composite articles can be made by disposing the conductivecurable composition onto at least one surface of the polymeric substrateat a temperature less than the boiling point of water (100° C.), andthen concurrently curing the thermally conductive thermal radical curesilicone compositions and bonding it to the polymeric substrate(s). Thisobviates the need to pre-dry the substrate(s). Composite articles canalso be cured and bonded in a similar fashion at room temperature thateliminates the need to use a curing oven.

Mixing and dispensing of multi-component compositions can be carried outin several ways. For example, the compositions can be mixed at thedesired volume ratio in air in a bag or through a pressurized gun. It isbeneficial to tailor the viscosity and density of thermally conductivethermal radical cure silicone compositions to allow for their efficientmixing and dispensing. Fillers of varying density and viscositymodifiers such as solvents, monomers, and polymers can be used to impartcontrol of these properties. It is also beneficial to exclude oxygenfrom the environment in the mixing device before dispensing it on asubstrate to minimize pre-mature curing and plugging of the mixing anddispensing device.

The thermally conductive thermal radical cure silicone compositions ofthe invention are useful for preparing electrically conductive rubbers,electrically conductive tapes, electrically conductive curableadhesives, electrically conductive foams, and electrically conductivepressure sensitive adhesives. The thermally conductive thermal radicalcure silicone compositions are especially useful for preparingelectrically conductive silicone adhesives. Electrically conductivesilicone adhesives have numerous uses including die attach adhesives,solder replacements, and electrically conductive coatings and gaskets.In particular, electrically conductive silicone adhesives are useful forbonding electronic components to flexible or rigid substrates.

The thermally conductive thermal radical cure silicone compositions canalso be used for the assembly of electronic components, as substitutesfor soldering, as electrical and thermal interface materials, and asconductive inks. The thermally conductive thermal radical cure siliconecompositions can be in the form of a rigid part or a flexible elastomer,and can be dispensed, pre-cured in rolls or sheet form as films, such aspressure sensitive adhesives. They can also be dispensed and cured inplace in the final application. Foamed thermally conductive thermalradical cure silicone compositions can be used as gaskets and seals inapplications such as electrical and electronic housings to prevent thetransmission of electromagnetic and radio frequency noise across thesealed areas.

The thermally conductive thermal radical cure silicone compositions aresimilarly useful for preparing thermally conductive rubbers, thermallyconductive tapes, thermally conductive curable adhesives, thermallyconductive foams, and thermally conductive pressure sensitive adhesives.The thermally conductive thermal radical cure silicone compositions areespecially useful for preparing thermally conductive silicone adhesives.Thermally conductive thermal radical cure silicone compositions haveseveral uses including their use as die attach adhesives, solderreplacements, and thermally conductive coatings and gaskets. Thermallyconductive thermal radical cure silicone compositions are especiallyuseful for bonding electronic components to flexible or rigidsubstrates.

Thermally conductive thermal radical cure silicone compositions can alsobe used for assembling electronic components, as substitutes forsoldering, as thermal interface materials, and as thermally conductiveinks or greases. The thermally conductive thermal radical cure siliconecompositions can be in the form of a rigid part or in the form of aflexible elastomer and can be dispensed, pre-cured in rolls or in sheetsas films, such as pressure sensitive adhesives. They can also bedisplaced and cured in place in the final application. Partially curedthermally conductive thermal radical cure silicone compositions can beused as thermally conductive greases. Foamed thermally conductivethermal radical cure silicone compositions can be used as gaskets andseals in electrical and electronic housings. When the thermallyconductive thermal radical cure silicone composition is a thermallyconductive adhesive, the conductive curable composition offersparticular advantages as a thermal interface material to provide goodbonding strength between heat sinks, heat spreaders, or heat dissipationdevices, particularly where the heat sink or heat dissipation device hasa polymeric-matrix.

So that those skilled in the art can understand and appreciate theinvention taught herein, the following examples are presented, it beingunderstood that these examples should not be used to limit the scope ofthis invention found in the claims attached hereto. All parts andpercentages in the examples are on a weight basis and all measurementswere obtained at 25° C., unless indicated to the contrary.

Comparative Examples

These examples are intended to illustrate the invention to one ofordinary skill in the art and should not be interpreted as limiting thescope of the invention set forth in the claims.

NMR:

Solution-state ²⁹Si- and ¹³C-NMR spectra were recorded on a Mercury VX400 MHz spectrometer at room temperature (20-22° C.) using CDCl3(Isotec) in a 16 mm Si-free probe. Cr(acac)₃ (Chromium acetylacetonoate)(20 mM) was added to NMR samples as a relaxation agent. ²⁹Si NMR spectrawere acquired at 79.493 MHz and processed with 5 Hz of Lorentzian linebroadening. The spectra were only semiquantitative due to the longrelaxation times of the ²⁹Si nucleus, but relative comparison of spectraacquired under identical conditions was considered quantitative. ¹³C NMRspectra were acquired at 100.626 MHz and processed with 3 Hz ofLorentzian line broadening. For both nuclei, 256-512 scans with a 90°pulse width were typically co-added to achieve adequate sensitivity; a6-second (²⁹Si) or 12-second (13C) delay between pulses was used. Gateddecoupling was used to remove negative nuclear Overhauser effects.Chemical shifts were referenced to external tetramethylsilane (TMS).

I. List of Components for Examples

DOW CORNING® SFD-119; 0.46 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-117; 0.2 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-120; 0.13 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® SFD-128; 0.088 wt % vinyl linear polydimethylsiloxane;

DOW CORNING® Q2-5057S; 0.15 wt % SiH methylhydrogen silicone, linear;

DOW CORNING® Q2-556S; 0.027 wt % SiH methylhydrogen silicone, linear;

Methylhydrogensiloxane; 1.67 wt % SiH methylhydrogen silicone cyclic;

DOW CORNING® 2-0707; Platinum catalyst 0.52 wt % Platinum;

MB2030—(DOW CORNING® SFD-128/silica blend);

Methyltrimethoxysilane (MTM); DOW CORNING® Z6070;

OFS-1579/ETS900—Mixture of methyl and ethyltriacetoxysilane;

DOW CORNING® Z-6030 SILANE Methacryloxypropyltrimethoxysilane;

DOW CORNING® Z-2306 SILANE Isobutyltrimethoxysilane (IBTMS);

DOW CORNING® Z-6341SILANE n-octyltriethoxysilane (nOTE);

Diallyl Maleate (DAM) available from from Bimax Inc. of Glen Rock, Pa.;

Allyl methacrylate (AMA) available from BASF Corporation of FlorhamPark, N.J.

Butylated Hydroxy Toluene (BHT) available from from Sigma Aldrich ofMilwaukee, Wis.;

Magnesium oxide (MAGOX SUPER PREMIUM); available from Premier Magnesia,W. Conshohocken, Pa. 19428 USAA;

DAW-45; aluminum oxide filler commercially available from Denka;

AL-43-ME; aluminum oxide filler commercially available from Showo-Denko;

CB-A20S; aluminum oxide filler commercially available from Showo-Denko;

Varox® DCBP-50 Paste; available from R T Vanderbilt Co., Norwalk Conn.06856 USA;

Perkadox L-50-PS; a product of Azko Nobel Polymer LLC, Chicago Ill. USA;

TAIC; triallylisocyanurate from Sigma-Aldrich Corp. St. Louis, Mo., USA;

TYZOR TNBT; available from Dorf Ketal Speciality Catalysts, LLC, 3727Greenbriar Dr., Stafford, Tex. 77477 USA;

TINOPAL OB, Optical brightener from BASF Corporation 100 Campus DriveFlorham Park, N.J. 07932. USA;

DOW CORNING® TC 1-4173 is a 1-part platinum addition-cured thermallyconductive adhesive.

II. Impact of Isomer Reducing Agent on A Silicone Reactive Diluent(Samples 1 and 2)

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 gof BHT, and 318.69 g of AMA were loaded. The mixture was inerted using2% oxygen in nitrogen atmosphere and stirred for 10 minutes, at whichpoint 6.64 g of a platinum catalyst was added. The mixture was stirredfor 10 additional minutes before setting the temperature at 50° C. Thetemperature was held for 30 minutes at 50° C. before adding 9.96 g ofDAM. The mixture was stirred for 10 additional minutes. The temperaturewas held for 30 minutes at 50° C. at a vacuum of 75 Torr. The resutantcomposition (Sample 1) was cooled to less than 30° C. before packaging.

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 gof BHT, 318.69 g of AMA, and 1.3 g of OFS-1579 isomer reducing agentwere loaded. The mixture was inerted using 2% oxygen in nitrogenatmosphere and stirred for 10 minutes, at which point 6.64 g of aplatinum catalyst was added. The mixture was stirred for 10 additionalminutes before setting the temperature at 50° C. The temperature washeld for 30 minutes at 50° C. before adding 9.96 g of DAM. The mixturewas then stirred for 10 additional minutes. The temperature was held for30 minutes at 50° C. at a vacuum of 75 Torr. The resutant composition(Sample 2) was cooled to less than 30° C. before packaging.

Samples 1 and 2 were measured for viscosity (in centipoises (cps)) usinga Brookfield LVF viscometer at 60 revolutions per minute using a #3spindle. The results, as shown in Table 3, indicate that theintroduction of the isomer reducing agent (Sample 2) provided arelatively stable viscosity over a 90 days period, while the viscosityof the corresponding example (Sample 1) without the isomer reducingagent increased to almost double the viscosity after 90 days.

TABLE 1 Days of aging Initial 91 Sample 1 240 cp 400 cp Sample 2 250 cp250 cp

III. Preparation of Thermally Conductive Thermal Radical Cure SiliconeAdhesive

A: Preparation of Thermally Conductive Clustered FunctionalPolyorganosiloxane (TC CFP) with Isomer Reducing Agent

In a 1 quart Gallon Baker Perkin mixer, 133.2 g of DOW CORNING® SFD120polymer, 991 g of Al-43-ME (Al2O3 filler), 99.1 g of DAW-45 (Al2O3filler) and 35.8 g of DOW CORNING® Z-6341 (filler treat agent) wereloaded. During the loading, Al-43-ME and Z-6341 were loaded in 3 stepsto reach the total amount described above. In between the 3-steploadings, there was 2-5 mins mixing at room temperature to mesh in thefillers. After all material (described above) added in the mixer, themixture was blended for 20 minutes before setting the temperature at149° C. The temperature was held for 30 minutes at 149° C. with a vacuumand N2. The mixture was then cooled to lower than 30° C. A homogenizedpremixture of 3.93 g of cyclic methylhydrogensiloxane, and 7.94 g ofchain extender Q2-5057S, 0.025 g of BHT, 12.25 g of AMA, and 0.025 g ofOFS-1579 isomer reducing agent were loaded. The mixture was blended foran additional 10 minutes at room temperature, at which point 0.18 g of aplatinum catalyst was added. The mixture was blended for 10 additionalminutes before setting the temperature at 80° C. The temperature washeld for 30 minutes at 80° C. before cooling to lower than 50° C. andadding 0.27 g of DAM. The mixture was blended for 5 additional minutesbefore setting the temperature at 50° C. The temperature was held for 15minutes at 50° C. and a vacuum. The mixture was then cooled to less than35° C. before packaging. The resultant polymer is hereinafter referredto as TC CFP.

B. Synthesis Silicone Reactive Diluent (SRD-1)

In a 50 liter Turello mixer, 6196.7 g of chain extender Q2-5567S, 1.3 gof BHT, 318.69 g of AMA, and 1.3 g of OFS-1579 isomer reducing agentwere loaded. The mixture was inerted using 2% oxygen in nitrogenatmosphere and stirred for 10 minutes, at which point 6.64 g of aplatinum catalyst was added and the mixture. The mixture was stirred for10 additional minutes before setting the temperature at 50° C. Thetemperature was held for 30 minutes at 50° C. before adding 9.96 g ofDAM. The mixture was stirred for 10 additional minutes. The temperaturewas held for 30 minutes at 50° C. and a vacuum of 75 Torr. The mixturewas then cooled to less than 35° C. The resultant polymer is hereinafterreferred to as SRD-1.

C. Preparation of Thermally Conductive Adhesives (TCA)

599 g of TC CFP, 645.9 g of DAW-45 (Al2O3 filler), 3.5 g of MgO2 and134.3 g of SRD-1 were added in a 1 quart Gallon Baker Perkin mixer. Themixture (M-5) was mixed for 30 minutes at room temperature (<30° C.)with a vacuum. Adhesive compositions were prepared by further addingpromoter packages and radical initiators as provided in Table 2 below.

TABLE 2 Thermally conductive adhesive (TCA) formulation (unit in gram)M-5 1382.7 Z-6030 Silane¹ 7 Z-6040 TAIC Z-2306 Silane² 2.07 TYZOR TNBT³0.69 Allyl Methacrylate 0.45 Varox DCBP-50 Paste 7

IV. Evaluation of Physical Properties of Adhesive Composition

Viscosity measurement on TCA formulations: In the following examples, aBrooksfield cone and plane viscometer (DV-II, spindle #52, speed 2 rpm)and a Brooksfield RVF viscometer (spindle #7, speed 2 rpm (low shear)and 20 rpm (high shear)) were utilized to determine the viscosity of thevarious thermally conductive adhesive formulations.

Sample Preparation on Alclad™ Panels:

1″×3″ Al Alclad™ Panels (available from Alcoa) were cleaned with acetone(3 samples prepared). Bondlines were established using Spheriglassspacer beads (Potters Industries Inc. 350 North Baker Drive, Canby,Oreg. 97013-0607) appropriate with the application (i.e, 23 mil).

Next, the adhesives were applied to Alclad™ aluminum substrates. Two ⅜″binder clip were used with spacer methods to secure substrates duringcure. The Cure condition was 30 minutes at 85° C. One half of thesamples were evaluated at room temperature and aged, while the remainingsamples were placed in 150° C. oven for 3 days.

Testing was carried out on Instron 5566 tensiometer at 2 inches perminute (Instron Worldwide Headquarters, 825 University Ave, Norwood,Mass. 02062-2643). The lap shear adhesive properties of the coatedsubstrates were evaluated for peak stress, in pounds per square inch(PSI), with the results summarized in Table 6-8 below.

Prepare Thermally Conductive Adhesive (TCA) Formulation Samples forPhysical Test and Thermal Conductivity:

TCA material in dental cup was removed from freezer and allowed to warmup to near room temp for at least one hour. Cup of material then placedin chamber and full vacuum was pulled for 15 minutes. Approximately56-58 g of material was then poured carefully into 4″×4″×0.075″ chase totry and minimize introduction of air into material. The chase was usedalong with Teflon sheets on each side to help with the release ofmaterial and to produce smooth surfaces, and two backing plates to helpshape the slab. The chase, between the two backing plates was thenplaced into the Dake hot press at 85° C. and 10 tons of force for 30minutes.

After cure, material was removed from the hot press and allowed to coolto room temperature. Then the slab of material was trimmed around theedges and removed from the chase. From this slab, using a “dogbone”shaped cutter and press, 5 samples were cut for tensile and elongationtesting. Three (labeled RT samples) were tested 24 hours after cure. Theremaining two samples were exposed to 150° C. for 3 days before testingand were labeled TRT samples.

The Instron T2000 tensometer was used to perform the physical testing,with the test program titled “Standard Tensile Test”. Then used theleftovers from the slab (pieces that were not pulled) for Durometer andthermal conductivity measurement. The stack of three pieces reached 6 mmthickness (ref as the stack). For Shore A Durometer, 5 readings weretaken. For HotDisk thermal tester (TPS 2500S Therm Test Inc), two stackswere placed on the top and bottom of thermal test probe. The measurementwas taken with the setting as output powder 0.25 w and time measure 10s.

TABLE 3 Viscosity (before cure) Viscosity at Viscosity at high low shearshear TCA from M-5 in Table 2 220e3 cp 76e3 cp Dow Corning ® TC 1-4173230e3 cp 63e3 cp

As Table 3 confirms, the adhesive composition (Table 2 Adhesives)according to the present invention exhibited similar rheology propertieswere achieved by compositions of the invention.

TABLE 4 Properties after cure TCA from M-5 in Dow Corning ® TC Table 21-4173 Cure condition 85° C. for 30 mins 150° C. for 30 mins Thermalconductivity 1.87 1.81 (W/mK) Shore A Durometer 91 92 Elongation, % 24.931.7 Tensile Strength, psi 713 714 Lap shear to Alclad ™ Al, psi 619 579percentage cohesive failure 80% 100% after lap shear pull

As Table 4 confirms, the adhesive composition (Table 2 Adhesives)according to the present invention exhibited >1.5 W/mK thermalconductivity, adequate physical properties in terms of Durometerhardness, tensile strength, elongation, and lap shear on Alclad™ Alsubstrates. In addition, the adhesive composition (Table 2 Adhesives)according to the present invention cured at lower temperatures (actualcure condition or bond line cure condition) than platinum catalyzedaddition chemistry adhesive systems. The introduction of siliconereactive diluents to the adhesive formulation retained the cure profileat low temperature 85° C. for 30 mins.

The instant disclosure has been described in an illustrative manner, andit is to be understood that the terminology which has been used isintended to be in the nature of words of description rather than oflimitation. Obviously, many modifications and variations of the instantdisclosure are possible in light of the above teachings. It is,therefore, to be understood that within the scope of the appendedclaims, the instant disclosure may be practiced otherwise than asspecifically described.

The invention claimed is:
 1. A method for forming a thermally conductivethermal radical cure silicone composition, the method comprising: (a)forming a thermally conductive clustered functional polymer comprisingthe reaction product of a reaction of: a polyorganosiloxane having anaverage, per molecule, of at least 2 aliphatically unsaturated organicgroups, a polyorganohydrogensiloxane having an average of 4 to 15silicon atoms per molecule, a reactive species having, per molecule, atleast 1 aliphatically unsaturated organic group and 1 or more thermalradical curable groups, in the presence of a filler treating agent, afiller comprising a thermally conductive filler, an isomer reducingagent, and a hydrosilylation catalyst; and (b) blending the thermallyconductive clustered functional polymer with a radical initiator to formthe thermally conductive thermal radical cure silicone composition,wherein forming the thermally conductive clustered functional polymer of(a) comprises: (c) forming a first mixture comprising a thermallyconductive filler, a filler treating agent, and a polyorganosiloxanehaving an average, per molecule, of at least 2 aliphatically unsaturatedorganic groups; (d) heating the first mixture to a temperature from 50°C. to 300° C. to treat the thermally conductive filler with the fillertreating agent in the presence of the polyorganosiloxane; (e) coolingthe first mixture to a temperature below 30° C.; (f) introducing thefollowing components to the first mixture to form a second mixture: apolyorganohydrogensiloxane having an average of 4 to 15 silicon atomsper molecule a reactive species having, per molecule, at least 1aliphatically unsaturated organic group and 1 or more thermal radicalcurable groups, an isomer reducing agent, and a hydrosilylationcatalyst; (g) shearing the second mixture; and (h) heating the secondmixture to a temperature ranging from 50° C. to 100° C. for a sufficienttime such that substantially all of the Si—H groups of the secondmixture have reacted.
 2. The method according to claim 1 furthercomprising: (i) cooling the second mixture to below 50° C.; (j) mixing asilicone reactive diluent and an additional amount of the thermallyconductive filler and an additional amount of filler treating agent withthe thermally conductive clustered functional polymer after step (i) andprior to step (b) to form a third mixture; (k) heating the third mixtureto a temperature from 50° C. to 110° C. to in situ treat the additionalamount of thermally conductive filler with the additional amount offiller treating agent in the presence of the silicone reactive diluent.3. The method according to claim 2, wherein the silicone reactivediluent comprises the reaction product of a reaction of: a) apolyorganohydrogensiloxane having an average of 10 to 200 silicon atomsper molecule, and b) a second reactive species having, per molecule, atleast 1 aliphatically unsaturated organic group and 1 or more curablegroups, in the presence of c) a second isomer reducing agent and d) asecond hydrosilylation catalyst and e) inhibitor for the secondhydrosilylation catalyst.
 4. The method according to claim 2, whereinthe silicone reactive diluent comprising the reaction product of areaction of: a) a siloxane compound according to the formula:

wherein: R is a monovalent hydrocarbon having 1 to 6 carbon atoms, R′ isa monovalent hydrocarbon having 3 to 12 carbon atoms, R″ is H or CH_(3′)and the subscript m and n each independently have a value from 1 to 10,and b) a second polyorganosiloxane having an average, per molecule, ofat least 2 aliphatically unsaturated organic groups, in the presence ofc) a second hydrosilylation catalyst and d) an inhibitor for the secondhydrosilylation catalyst.
 5. The method according to claim 1 furthercomprising: (i) mixing a silicone reactive diluent with the thermallyconductive clustered functional polymer after step (h) and prior to step(b) (j) cooling the second mixture to below 50° C.; (k) mixing anadditional amount of the thermally conductive filler and an additionalamount of filler treating agent with the thermally conductive clusteredfunctional polymer after step (j) and prior to step (b) to form a thirdmixture; (l) heating the third mixture to a temperature from 50° C. to110° C. to in situ treat the additional amount of thermally conductivefiller with the additional amount of filler treating agent in thepresence of the silicone reactive diluent.
 6. The method according toclaim 5, wherein the silicone reactive diluent comprises the reactionproduct of a reaction of: a) a polyorganohydrogensiloxane having anaverage of 10 to 200 silicon atoms per molecule, and b) a secondreactive species having, per molecule, at least 1 aliphaticallyunsaturated organic group and 1 or more curable groups, in the presenceof c) a second isomer reducing agent and d) a second hydrosilylationcatalyst and e) inhibitor for the second hydrosilylation catalyst. 7.The method according to claim 5, wherein the silicone reactive diluentcomprising the reaction product of a reaction of: a) a siloxane compoundaccording to the formula:

wherein: R is a monovalent hydrocarbon having 1 to 6 carbon atoms, R′ isa monovalent hydrocarbon having 3 to 12 carbon atoms, R″ is H or CH_(3′)and the subscript m and n each independently have a value from 1 to 10,and b) a second polyorganosiloxane having an average, per molecule, ofat least 2 aliphatically unsaturated organic groups, in the presence ofc) a second hydrosilylation catalyst and d) an inhibitor for the secondhydrosilylation catalyst.
 8. The method according to claim 1 furthercomprising (m) blending at least one additional component with thethermally conductive clustered functional polymer prior to step (b), theat least one component selected from the group consisting of (V) amoisture cure initiator, (VI) a crosslinker, (VII) a moisture curepolymer, (VIII) a solvent, (IX) an adhesion promoter, (X) a colorant,(XI) a reactive diluent, (XII) a corrosion inhibitor, (XIII) apolymerization inhibitor, (XIV) an acid acceptor, and any combinationthereof.
 9. The method as set forth in claim 8, wherein the (VI)crosslinker and the moisture cure polymer (VII) are both present inthermally conductive thermal radical cure silicone composition andwherein the amount of the crosslinker (VI) comprises from 0.001 to 50weight percent of the total weight of moisture cure polymer (VII) andwherein the amount of the moisture cure polymer (VII) comprises from 0.1to 5 weight percent of the total weight of thermally conductive thermalradical cure silicone composition.
 10. The method according to claim 1,wherein the thermally conductive filler comprises from 30 to 80 volumepercent of the total volume of the thermally conductive thermal radicalcure silicone composition.
 11. The method as set forth in claim 10,wherein the (VI) crosslinker and the moisture cure polymer (VII) areboth present in thermally conductive thermal radical cure siliconecomposition and wherein the amount of the crosslinker (VI) comprisesfrom 0.001 to 50 weight percent of the total weight of moisture curepolymer (VII) and wherein the amount of the moisture cure polymer (VII)comprises from 0.1 to 5 weight percent of the total weight of thermallyconductive thermal radical cure silicone composition.
 12. The method asset forth in claim 1, wherein the thermally conductive thermal radicalcure silicone composition has a thermal conductivity greater than 0.5watts per meter kelvin.
 13. A method for forming a conductive curedsubstrate comprising: (a) forming a thermally conductive thermal radicalcure silicone composition in accordance with the method of claim 1; (b)applying the thermally conductive thermal radical cure siliconecomposition to a substrate; and (c) curing the thermally conductivethermal radical cure silicone composition on the substrate to form theconductive cured substrate.
 14. A method for forming a cured thermallyconductive thermal radical cure silicone composition comprising: (a)forming a thermally conductive thermal radical cure silicone compositionin accordance with the method of claim 1; and (b) curing the thermallyconductive thermal radical cure silicone composition.